summaryrefslogtreecommitdiffstats
path: root/Lib/importlib/_bootstrap.py
blob: 5b91c0538194e0a8a0b4d6e86e85dfd0f7141f8b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
"""Core implementation of import.

This module is NOT meant to be directly imported! It has been designed such
that it can be bootstrapped into Python as the implementation of import. As
such it requires the injection of specific modules and attributes in order to
work. One should use importlib as the public-facing version of this module.

"""
#
# IMPORTANT: Whenever making changes to this module, be sure to run
# a top-level make in order to get the frozen version of the module
# update. Not doing so will result in the Makefile to fail for
# all others who don't have a ./python around to freeze the module
# in the early stages of compilation.
#

# See importlib._setup() for what is injected into the global namespace.

# When editing this code be aware that code executed at import time CANNOT
# reference any injected objects! This includes not only global code but also
# anything specified at the class level.

# Bootstrap-related code ######################################################

_CASE_INSENSITIVE_PLATFORMS = 'win', 'cygwin', 'darwin'


def _make_relax_case():
    if sys.platform.startswith(_CASE_INSENSITIVE_PLATFORMS):
        def _relax_case():
            """True if filenames must be checked case-insensitively."""
            return b'PYTHONCASEOK' in _os.environ
    else:
        def _relax_case():
            """True if filenames must be checked case-insensitively."""
            return False
    return _relax_case


def _w_long(x):
    """Convert a 32-bit integer to little-endian."""
    return (int(x) & 0xFFFFFFFF).to_bytes(4, 'little')


def _r_long(int_bytes):
    """Convert 4 bytes in little-endian to an integer."""
    return int.from_bytes(int_bytes, 'little')


def _path_join(*path_parts):
    """Replacement for os.path.join()."""
    return path_sep.join([part.rstrip(path_separators)
                          for part in path_parts if part])


def _path_split(path):
    """Replacement for os.path.split()."""
    if len(path_separators) == 1:
        front, _, tail = path.rpartition(path_sep)
        return front, tail
    for x in reversed(path):
        if x in path_separators:
            front, tail = path.rsplit(x, maxsplit=1)
            return front, tail
    return '', path


def _path_stat(path):
    """Stat the path.

    Made a separate function to make it easier to override in experiments
    (e.g. cache stat results).

    """
    return _os.stat(path)


def _path_is_mode_type(path, mode):
    """Test whether the path is the specified mode type."""
    try:
        stat_info = _path_stat(path)
    except OSError:
        return False
    return (stat_info.st_mode & 0o170000) == mode


def _path_isfile(path):
    """Replacement for os.path.isfile."""
    return _path_is_mode_type(path, 0o100000)


def _path_isdir(path):
    """Replacement for os.path.isdir."""
    if not path:
        path = _os.getcwd()
    return _path_is_mode_type(path, 0o040000)


def _write_atomic(path, data, mode=0o666):
    """Best-effort function to write data to a path atomically.
    Be prepared to handle a FileExistsError if concurrent writing of the
    temporary file is attempted."""
    # id() is used to generate a pseudo-random filename.
    path_tmp = '{}.{}'.format(path, id(path))
    fd = _os.open(path_tmp,
                  _os.O_EXCL | _os.O_CREAT | _os.O_WRONLY, mode & 0o666)
    try:
        # We first write data to a temporary file, and then use os.replace() to
        # perform an atomic rename.
        with _io.FileIO(fd, 'wb') as file:
            file.write(data)
        _os.replace(path_tmp, path)
    except OSError:
        try:
            _os.unlink(path_tmp)
        except OSError:
            pass
        raise


def _wrap(new, old):
    """Simple substitute for functools.update_wrapper."""
    for replace in ['__module__', '__name__', '__qualname__', '__doc__']:
        if hasattr(old, replace):
            setattr(new, replace, getattr(old, replace))
    new.__dict__.update(old.__dict__)


def _new_module(name):
    return type(sys)(name)


_code_type = type(_wrap.__code__)



class _ManageReload:

    """Manages the possible clean-up of sys.modules for load_module()."""

    def __init__(self, name):
        self._name = name

    def __enter__(self):
        self._is_reload = self._name in sys.modules

    def __exit__(self, *args):
        if any(arg is not None for arg in args) and not self._is_reload:
            try:
                del sys.modules[self._name]
            except KeyError:
                pass

# Module-level locking ########################################################

# A dict mapping module names to weakrefs of _ModuleLock instances
_module_locks = {}
# A dict mapping thread ids to _ModuleLock instances
_blocking_on = {}


class _DeadlockError(RuntimeError):
    pass


class _ModuleLock:
    """A recursive lock implementation which is able to detect deadlocks
    (e.g. thread 1 trying to take locks A then B, and thread 2 trying to
    take locks B then A).
    """

    def __init__(self, name):
        self.lock = _thread.allocate_lock()
        self.wakeup = _thread.allocate_lock()
        self.name = name
        self.owner = None
        self.count = 0
        self.waiters = 0

    def has_deadlock(self):
        # Deadlock avoidance for concurrent circular imports.
        me = _thread.get_ident()
        tid = self.owner
        while True:
            lock = _blocking_on.get(tid)
            if lock is None:
                return False
            tid = lock.owner
            if tid == me:
                return True

    def acquire(self):
        """
        Acquire the module lock.  If a potential deadlock is detected,
        a _DeadlockError is raised.
        Otherwise, the lock is always acquired and True is returned.
        """
        tid = _thread.get_ident()
        _blocking_on[tid] = self
        try:
            while True:
                with self.lock:
                    if self.count == 0 or self.owner == tid:
                        self.owner = tid
                        self.count += 1
                        return True
                    if self.has_deadlock():
                        raise _DeadlockError('deadlock detected by %r' % self)
                    if self.wakeup.acquire(False):
                        self.waiters += 1
                # Wait for a release() call
                self.wakeup.acquire()
                self.wakeup.release()
        finally:
            del _blocking_on[tid]

    def release(self):
        tid = _thread.get_ident()
        with self.lock:
            if self.owner != tid:
                raise RuntimeError('cannot release un-acquired lock')
            assert self.count > 0
            self.count -= 1
            if self.count == 0:
                self.owner = None
                if self.waiters:
                    self.waiters -= 1
                    self.wakeup.release()

    def __repr__(self):
        return '_ModuleLock({!r}) at {}'.format(self.name, id(self))


class _DummyModuleLock:
    """A simple _ModuleLock equivalent for Python builds without
    multi-threading support."""

    def __init__(self, name):
        self.name = name
        self.count = 0

    def acquire(self):
        self.count += 1
        return True

    def release(self):
        if self.count == 0:
            raise RuntimeError('cannot release un-acquired lock')
        self.count -= 1

    def __repr__(self):
        return '_DummyModuleLock({!r}) at {}'.format(self.name, id(self))


class _ModuleLockManager:

    def __init__(self, name):
        self._name = name
        self._lock = None

    def __enter__(self):
        try:
            self._lock = _get_module_lock(self._name)
        finally:
            _imp.release_lock()
        self._lock.acquire()

    def __exit__(self, *args, **kwargs):
        self._lock.release()


# The following two functions are for consumption by Python/import.c.

def _get_module_lock(name):
    """Get or create the module lock for a given module name.

    Should only be called with the import lock taken."""
    lock = None
    try:
        lock = _module_locks[name]()
    except KeyError:
        pass
    if lock is None:
        if _thread is None:
            lock = _DummyModuleLock(name)
        else:
            lock = _ModuleLock(name)
        def cb(_):
            del _module_locks[name]
        _module_locks[name] = _weakref.ref(lock, cb)
    return lock

def _lock_unlock_module(name):
    """Release the global import lock, and acquires then release the
    module lock for a given module name.
    This is used to ensure a module is completely initialized, in the
    event it is being imported by another thread.

    Should only be called with the import lock taken."""
    lock = _get_module_lock(name)
    _imp.release_lock()
    try:
        lock.acquire()
    except _DeadlockError:
        # Concurrent circular import, we'll accept a partially initialized
        # module object.
        pass
    else:
        lock.release()

# Frame stripping magic ###############################################

def _call_with_frames_removed(f, *args, **kwds):
    """remove_importlib_frames in import.c will always remove sequences
    of importlib frames that end with a call to this function

    Use it instead of a normal call in places where including the importlib
    frames introduces unwanted noise into the traceback (e.g. when executing
    module code)
    """
    return f(*args, **kwds)


# Finder/loader utility code ###############################################

# Magic word to reject .pyc files generated by other Python versions.
# It should change for each incompatible change to the bytecode.
#
# The value of CR and LF is incorporated so if you ever read or write
# a .pyc file in text mode the magic number will be wrong; also, the
# Apple MPW compiler swaps their values, botching string constants.
#
# The magic numbers must be spaced apart at least 2 values, as the
# -U interpeter flag will cause MAGIC+1 being used. They have been
# odd numbers for some time now.
#
# There were a variety of old schemes for setting the magic number.
# The current working scheme is to increment the previous value by
# 10.
#
# Starting with the adoption of PEP 3147 in Python 3.2, every bump in magic
# number also includes a new "magic tag", i.e. a human readable string used
# to represent the magic number in __pycache__ directories.  When you change
# the magic number, you must also set a new unique magic tag.  Generally this
# can be named after the Python major version of the magic number bump, but
# it can really be anything, as long as it's different than anything else
# that's come before.  The tags are included in the following table, starting
# with Python 3.2a0.
#
# Known values:
#  Python 1.5:   20121
#  Python 1.5.1: 20121
#     Python 1.5.2: 20121
#     Python 1.6:   50428
#     Python 2.0:   50823
#     Python 2.0.1: 50823
#     Python 2.1:   60202
#     Python 2.1.1: 60202
#     Python 2.1.2: 60202
#     Python 2.2:   60717
#     Python 2.3a0: 62011
#     Python 2.3a0: 62021
#     Python 2.3a0: 62011 (!)
#     Python 2.4a0: 62041
#     Python 2.4a3: 62051
#     Python 2.4b1: 62061
#     Python 2.5a0: 62071
#     Python 2.5a0: 62081 (ast-branch)
#     Python 2.5a0: 62091 (with)
#     Python 2.5a0: 62092 (changed WITH_CLEANUP opcode)
#     Python 2.5b3: 62101 (fix wrong code: for x, in ...)
#     Python 2.5b3: 62111 (fix wrong code: x += yield)
#     Python 2.5c1: 62121 (fix wrong lnotab with for loops and
#                          storing constants that should have been removed)
#     Python 2.5c2: 62131 (fix wrong code: for x, in ... in listcomp/genexp)
#     Python 2.6a0: 62151 (peephole optimizations and STORE_MAP opcode)
#     Python 2.6a1: 62161 (WITH_CLEANUP optimization)
#     Python 2.7a0: 62171 (optimize list comprehensions/change LIST_APPEND)
#     Python 2.7a0: 62181 (optimize conditional branches:
#                          introduce POP_JUMP_IF_FALSE and POP_JUMP_IF_TRUE)
#     Python 2.7a0  62191 (introduce SETUP_WITH)
#     Python 2.7a0  62201 (introduce BUILD_SET)
#     Python 2.7a0  62211 (introduce MAP_ADD and SET_ADD)
#     Python 3000:   3000
#                    3010 (removed UNARY_CONVERT)
#                    3020 (added BUILD_SET)
#                    3030 (added keyword-only parameters)
#                    3040 (added signature annotations)
#                    3050 (print becomes a function)
#                    3060 (PEP 3115 metaclass syntax)
#                    3061 (string literals become unicode)
#                    3071 (PEP 3109 raise changes)
#                    3081 (PEP 3137 make __file__ and __name__ unicode)
#                    3091 (kill str8 interning)
#                    3101 (merge from 2.6a0, see 62151)
#                    3103 (__file__ points to source file)
#     Python 3.0a4: 3111 (WITH_CLEANUP optimization).
#     Python 3.0a5: 3131 (lexical exception stacking, including POP_EXCEPT)
#     Python 3.1a0: 3141 (optimize list, set and dict comprehensions:
#             change LIST_APPEND and SET_ADD, add MAP_ADD)
#     Python 3.1a0: 3151 (optimize conditional branches:
#             introduce POP_JUMP_IF_FALSE and POP_JUMP_IF_TRUE)
#     Python 3.2a0: 3160 (add SETUP_WITH)
#                   tag: cpython-32
#     Python 3.2a1: 3170 (add DUP_TOP_TWO, remove DUP_TOPX and ROT_FOUR)
#                   tag: cpython-32
#     Python 3.2a2  3180 (add DELETE_DEREF)
#     Python 3.3a0  3190 __class__ super closure changed
#     Python 3.3a0  3200 (__qualname__ added)
#                      3210 (added size modulo 2**32 to the pyc header)
#     Python 3.3a1  3220 (changed PEP 380 implementation)
#     Python 3.3a4  3230 (revert changes to implicit __class__ closure)
#     Python 3.4a1  3250 (evaluate positional default arguments before
#                        keyword-only defaults)
#     Python 3.4a1  3260 (add LOAD_CLASSDEREF; allow locals of class to override
#                        free vars)
#     Python 3.4a1  3270 (various tweaks to the __class__ closure)
#     Python 3.4a1  3280 (remove implicit class argument)
#     Python 3.4a4  3290 (changes to __qualname__ computation)
#     Python 3.4a4  3300 (more changes to __qualname__ computation)
#     Python 3.4rc2 3310 (alter __qualname__ computation)
#
# MAGIC must change whenever the bytecode emitted by the compiler may no
# longer be understood by older implementations of the eval loop (usually
# due to the addition of new opcodes).

MAGIC_NUMBER = (3310).to_bytes(2, 'little') + b'\r\n'
_RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c

_PYCACHE = '__pycache__'

SOURCE_SUFFIXES = ['.py']  # _setup() adds .pyw as needed.

DEBUG_BYTECODE_SUFFIXES = ['.pyc']
OPTIMIZED_BYTECODE_SUFFIXES = ['.pyo']

def cache_from_source(path, debug_override=None):
    """Given the path to a .py file, return the path to its .pyc/.pyo file.

    The .py file does not need to exist; this simply returns the path to the
    .pyc/.pyo file calculated as if the .py file were imported.  The extension
    will be .pyc unless sys.flags.optimize is non-zero, then it will be .pyo.

    If debug_override is not None, then it must be a boolean and is used in
    place of sys.flags.optimize.

    If sys.implementation.cache_tag is None then NotImplementedError is raised.

    """
    debug = not sys.flags.optimize if debug_override is None else debug_override
    if debug:
        suffixes = DEBUG_BYTECODE_SUFFIXES
    else:
        suffixes = OPTIMIZED_BYTECODE_SUFFIXES
    head, tail = _path_split(path)
    base, sep, rest = tail.rpartition('.')
    tag = sys.implementation.cache_tag
    if tag is None:
        raise NotImplementedError('sys.implementation.cache_tag is None')
    filename = ''.join([(base if base else rest), sep, tag, suffixes[0]])
    return _path_join(head, _PYCACHE, filename)


def source_from_cache(path):
    """Given the path to a .pyc./.pyo file, return the path to its .py file.

    The .pyc/.pyo file does not need to exist; this simply returns the path to
    the .py file calculated to correspond to the .pyc/.pyo file.  If path does
    not conform to PEP 3147 format, ValueError will be raised. If
    sys.implementation.cache_tag is None then NotImplementedError is raised.

    """
    if sys.implementation.cache_tag is None:
        raise NotImplementedError('sys.implementation.cache_tag is None')
    head, pycache_filename = _path_split(path)
    head, pycache = _path_split(head)
    if pycache != _PYCACHE:
        raise ValueError('{} not bottom-level directory in '
                         '{!r}'.format(_PYCACHE, path))
    if pycache_filename.count('.') != 2:
        raise ValueError('expected only 2 dots in '
                         '{!r}'.format(pycache_filename))
    base_filename = pycache_filename.partition('.')[0]
    return _path_join(head, base_filename + SOURCE_SUFFIXES[0])


def _get_sourcefile(bytecode_path):
    """Convert a bytecode file path to a source path (if possible).

    This function exists purely for backwards-compatibility for
    PyImport_ExecCodeModuleWithFilenames() in the C API.

    """
    if len(bytecode_path) == 0:
        return None
    rest, _, extension = bytecode_path.rpartition('.')
    if not rest or extension.lower()[-3:-1] != 'py':
        return bytecode_path
    try:
        source_path = source_from_cache(bytecode_path)
    except (NotImplementedError, ValueError):
        source_path = bytecode_path[:-1]
    return source_path if _path_isfile(source_path) else bytecode_path


def _calc_mode(path):
    """Calculate the mode permissions for a bytecode file."""
    try:
        mode = _path_stat(path).st_mode
    except OSError:
        mode = 0o666
    # We always ensure write access so we can update cached files
    # later even when the source files are read-only on Windows (#6074)
    mode |= 0o200
    return mode


def _verbose_message(message, *args, verbosity=1):
    """Print the message to stderr if -v/PYTHONVERBOSE is turned on."""
    if sys.flags.verbose >= verbosity:
        if not message.startswith(('#', 'import ')):
            message = '# ' + message
        print(message.format(*args), file=sys.stderr)


def _check_name(method):
    """Decorator to verify that the module being requested matches the one the
    loader can handle.

    The first argument (self) must define _name which the second argument is
    compared against. If the comparison fails then ImportError is raised.

    """
    def _check_name_wrapper(self, name=None, *args, **kwargs):
        if name is None:
            name = self.name
        elif self.name != name:
            raise ImportError('loader cannot handle %s' % name, name=name)
        return method(self, name, *args, **kwargs)
    _wrap(_check_name_wrapper, method)
    return _check_name_wrapper


def _requires_builtin(fxn):
    """Decorator to verify the named module is built-in."""
    def _requires_builtin_wrapper(self, fullname):
        if fullname not in sys.builtin_module_names:
            raise ImportError('{!r} is not a built-in module'.format(fullname),
                              name=fullname)
        return fxn(self, fullname)
    _wrap(_requires_builtin_wrapper, fxn)
    return _requires_builtin_wrapper


def _requires_frozen(fxn):
    """Decorator to verify the named module is frozen."""
    def _requires_frozen_wrapper(self, fullname):
        if not _imp.is_frozen(fullname):
            raise ImportError('{!r} is not a frozen module'.format(fullname),
                              name=fullname)
        return fxn(self, fullname)
    _wrap(_requires_frozen_wrapper, fxn)
    return _requires_frozen_wrapper


def _find_module_shim(self, fullname):
    """Try to find a loader for the specified module by delegating to
    self.find_loader().

    This method is deprecated in favor of finder.find_spec().

    """
    # Call find_loader(). If it returns a string (indicating this
    # is a namespace package portion), generate a warning and
    # return None.
    loader, portions = self.find_loader(fullname)
    if loader is None and len(portions):
        msg = 'Not importing directory {}: missing __init__'
        _warnings.warn(msg.format(portions[0]), ImportWarning)
    return loader


def _load_module_shim(self, fullname):
    """Load the specified module into sys.modules and return it.

    This method is deprecated.  Use loader.exec_module instead.

    """
    spec = spec_from_loader(fullname, self)
    methods = _SpecMethods(spec)
    if fullname in sys.modules:
        module = sys.modules[fullname]
        methods.exec(module)
        return sys.modules[fullname]
    else:
        return methods.load()


def _validate_bytecode_header(data, source_stats=None, name=None, path=None):
    """Validate the header of the passed-in bytecode against source_stats (if
    given) and returning the bytecode that can be compiled by compile().

    All other arguments are used to enhance error reporting.

    ImportError is raised when the magic number is incorrect or the bytecode is
    found to be stale. EOFError is raised when the data is found to be
    truncated.

    """
    exc_details = {}
    if name is not None:
        exc_details['name'] = name
    else:
        # To prevent having to make all messages have a conditional name.
        name = '<bytecode>'
    if path is not None:
        exc_details['path'] = path
    magic = data[:4]
    raw_timestamp = data[4:8]
    raw_size = data[8:12]
    if magic != MAGIC_NUMBER:
        message = 'bad magic number in {!r}: {!r}'.format(name, magic)
        _verbose_message(message)
        raise ImportError(message, **exc_details)
    elif len(raw_timestamp) != 4:
        message = 'reached EOF while reading timestamp in {!r}'.format(name)
        _verbose_message(message)
        raise EOFError(message)
    elif len(raw_size) != 4:
        message = 'reached EOF while reading size of source in {!r}'.format(name)
        _verbose_message(message)
        raise EOFError(message)
    if source_stats is not None:
        try:
            source_mtime = int(source_stats['mtime'])
        except KeyError:
            pass
        else:
            if _r_long(raw_timestamp) != source_mtime:
                message = 'bytecode is stale for {!r}'.format(name)
                _verbose_message(message)
                raise ImportError(message, **exc_details)
        try:
            source_size = source_stats['size'] & 0xFFFFFFFF
        except KeyError:
            pass
        else:
            if _r_long(raw_size) != source_size:
                raise ImportError('bytecode is stale for {!r}'.format(name),
                                  **exc_details)
    return data[12:]


def _compile_bytecode(data, name=None, bytecode_path=None, source_path=None):
    """Compile bytecode as returned by _validate_bytecode_header()."""
    code = marshal.loads(data)
    if isinstance(code, _code_type):
        _verbose_message('code object from {!r}', bytecode_path)
        if source_path is not None:
            _imp._fix_co_filename(code, source_path)
        return code
    else:
        raise ImportError('Non-code object in {!r}'.format(bytecode_path),
                          name=name, path=bytecode_path)

def _code_to_bytecode(code, mtime=0, source_size=0):
    """Compile a code object into bytecode for writing out to a byte-compiled
    file."""
    data = bytearray(MAGIC_NUMBER)
    data.extend(_w_long(mtime))
    data.extend(_w_long(source_size))
    data.extend(marshal.dumps(code))
    return data


def decode_source(source_bytes):
    """Decode bytes representing source code and return the string.

    Universal newline support is used in the decoding.
    """
    import tokenize  # To avoid bootstrap issues.
    source_bytes_readline = _io.BytesIO(source_bytes).readline
    encoding = tokenize.detect_encoding(source_bytes_readline)
    newline_decoder = _io.IncrementalNewlineDecoder(None, True)
    return newline_decoder.decode(source_bytes.decode(encoding[0]))


# Module specifications #######################################################

def _module_repr(module):
    # The implementation of ModuleType__repr__().
    loader = getattr(module, '__loader__', None)
    if hasattr(loader, 'module_repr'):
        # As soon as BuiltinImporter, FrozenImporter, and NamespaceLoader
        # drop their implementations for module_repr. we can add a
        # deprecation warning here.
        try:
            return loader.module_repr(module)
        except Exception:
            pass
    try:
        spec = module.__spec__
    except AttributeError:
        pass
    else:
        if spec is not None:
            return _SpecMethods(spec).module_repr()

    # We could use module.__class__.__name__ instead of 'module' in the
    # various repr permutations.
    try:
        name = module.__name__
    except AttributeError:
        name = '?'
    try:
        filename = module.__file__
    except AttributeError:
        if loader is None:
            return '<module {!r}>'.format(name)
        else:
            return '<module {!r} ({!r})>'.format(name, loader)
    else:
        return '<module {!r} from {!r}>'.format(name, filename)


class _installed_safely:

    def __init__(self, module):
        self._module = module
        self._spec = module.__spec__

    def __enter__(self):
        # This must be done before putting the module in sys.modules
        # (otherwise an optimization shortcut in import.c becomes
        # wrong)
        self._spec._initializing = True
        sys.modules[self._spec.name] = self._module

    def __exit__(self, *args):
        try:
            spec = self._spec
            if any(arg is not None for arg in args):
                try:
                    del sys.modules[spec.name]
                except KeyError:
                    pass
            else:
                _verbose_message('import {!r} # {!r}', spec.name, spec.loader)
        finally:
            self._spec._initializing = False


class ModuleSpec:
    """The specification for a module, used for loading.

    A module's spec is the source for information about the module.  For
    data associated with the module, including source, use the spec's
    loader.

    `name` is the absolute name of the module.  `loader` is the loader
    to use when loading the module.  `parent` is the name of the
    package the module is in.  The parent is derived from the name.

    `is_package` determines if the module is considered a package or
    not.  On modules this is reflected by the `__path__` attribute.

    `origin` is the specific location used by the loader from which to
    load the module, if that information is available.  When filename is
    set, origin will match.

    `has_location` indicates that a spec's "origin" reflects a location.
    When this is True, `__file__` attribute of the module is set.

    `cached` is the location of the cached bytecode file, if any.  It
    corresponds to the `__cached__` attribute.

    `submodule_search_locations` is the sequence of path entries to
    search when importing submodules.  If set, is_package should be
    True--and False otherwise.

    Packages are simply modules that (may) have submodules.  If a spec
    has a non-None value in `submodule_search_locations`, the import
    system will consider modules loaded from the spec as packages.

    Only finders (see importlib.abc.MetaPathFinder and
    importlib.abc.PathEntryFinder) should modify ModuleSpec instances.

    """

    def __init__(self, name, loader, *, origin=None, loader_state=None,
                 is_package=None):
        self.name = name
        self.loader = loader
        self.origin = origin
        self.loader_state = loader_state
        self.submodule_search_locations = [] if is_package else None

        # file-location attributes
        self._set_fileattr = False
        self._cached = None

    def __repr__(self):
        args = ['name={!r}'.format(self.name),
                'loader={!r}'.format(self.loader)]
        if self.origin is not None:
            args.append('origin={!r}'.format(self.origin))
        if self.submodule_search_locations is not None:
            args.append('submodule_search_locations={}'
                        .format(self.submodule_search_locations))
        return '{}({})'.format(self.__class__.__name__, ', '.join(args))

    def __eq__(self, other):
        smsl = self.submodule_search_locations
        try:
            return (self.name == other.name and
                    self.loader == other.loader and
                    self.origin == other.origin and
                    smsl == other.submodule_search_locations and
                    self.cached == other.cached and
                    self.has_location == other.has_location)
        except AttributeError:
            return False

    @property
    def cached(self):
        if self._cached is None:
            if self.origin is not None and self._set_fileattr:
                filename = self.origin
                if filename.endswith(tuple(SOURCE_SUFFIXES)):
                    try:
                        self._cached = cache_from_source(filename)
                    except NotImplementedError:
                        pass
                elif filename.endswith(tuple(BYTECODE_SUFFIXES)):
                    self._cached = filename
        return self._cached

    @cached.setter
    def cached(self, cached):
        self._cached = cached

    @property
    def parent(self):
        """The name of the module's parent."""
        if self.submodule_search_locations is None:
            return self.name.rpartition('.')[0]
        else:
            return self.name

    @property
    def has_location(self):
        return self._set_fileattr

    @has_location.setter
    def has_location(self, value):
        self._set_fileattr = bool(value)


def spec_from_loader(name, loader, *, origin=None, is_package=None):
    """Return a module spec based on various loader methods."""
    if hasattr(loader, 'get_filename'):
        if is_package is None:
            return spec_from_file_location(name, loader=loader)
        search = [] if is_package else None
        return spec_from_file_location(name, loader=loader,
                                       submodule_search_locations=search)

    if is_package is None:
        if hasattr(loader, 'is_package'):
            try:
                is_package = loader.is_package(name)
            except ImportError:
                is_package = None  # aka, undefined
        else:
            # the default
            is_package = False

    return ModuleSpec(name, loader, origin=origin, is_package=is_package)


_POPULATE = object()


def spec_from_file_location(name, location=None, *, loader=None,
                            submodule_search_locations=_POPULATE):
    """Return a module spec based on a file location.

    To indicate that the module is a package, set
    submodule_search_locations to a list of directory paths.  An
    empty list is sufficient, though its not otherwise useful to the
    import system.

    The loader must take a spec as its only __init__() arg.

    """
    if location is None:
        # The caller may simply want a partially populated location-
        # oriented spec.  So we set the location to a bogus value and
        # fill in as much as we can.
        location = '<unknown>'
        if hasattr(loader, 'get_filename'):
            # ExecutionLoader
            try:
                location = loader.get_filename(name)
            except ImportError:
                pass

    # If the location is on the filesystem, but doesn't actually exist,
    # we could return None here, indicating that the location is not
    # valid.  However, we don't have a good way of testing since an
    # indirect location (e.g. a zip file or URL) will look like a
    # non-existent file relative to the filesystem.

    spec = ModuleSpec(name, loader, origin=location)
    spec._set_fileattr = True

    # Pick a loader if one wasn't provided.
    if loader is None:
        for loader_class, suffixes in _get_supported_file_loaders():
            if location.endswith(tuple(suffixes)):
                loader = loader_class(name, location)
                spec.loader = loader
                break
        else:
            return None

    # Set submodule_search_paths appropriately.
    if submodule_search_locations is _POPULATE:
        # Check the loader.
        if hasattr(loader, 'is_package'):
            try:
                is_package = loader.is_package(name)
            except ImportError:
                pass
            else:
                if is_package:
                    spec.submodule_search_locations = []
    else:
        spec.submodule_search_locations = submodule_search_locations
    if spec.submodule_search_locations == []:
        if location:
            dirname = _path_split(location)[0]
            spec.submodule_search_locations.append(dirname)

    return spec


def _spec_from_module(module, loader=None, origin=None):
    # This function is meant for use in _setup().
    try:
        spec = module.__spec__
    except AttributeError:
        pass
    else:
        if spec is not None:
            return spec

    name = module.__name__
    if loader is None:
        try:
            loader = module.__loader__
        except AttributeError:
            # loader will stay None.
            pass
    try:
        location = module.__file__
    except AttributeError:
        location = None
    if origin is None:
        if location is None:
            try:
                origin = loader._ORIGIN
            except AttributeError:
                origin = None
        else:
            origin = location
    try:
        cached = module.__cached__
    except AttributeError:
        cached = None
    try:
        submodule_search_locations = list(module.__path__)
    except AttributeError:
        submodule_search_locations = None

    spec = ModuleSpec(name, loader, origin=origin)
    spec._set_fileattr = False if location is None else True
    spec.cached = cached
    spec.submodule_search_locations = submodule_search_locations
    return spec


class _SpecMethods:

    """Convenience wrapper around spec objects to provide spec-specific
    methods."""

    # The various spec_from_* functions could be made factory methods here.

    def __init__(self, spec):
        self.spec = spec

    def module_repr(self):
        """Return the repr to use for the module."""
        # We mostly replicate _module_repr() using the spec attributes.
        spec = self.spec
        name = '?' if spec.name is None else spec.name
        if spec.origin is None:
            if spec.loader is None:
                return '<module {!r}>'.format(name)
            else:
                return '<module {!r} ({!r})>'.format(name, spec.loader)
        else:
            if spec.has_location:
                return '<module {!r} from {!r}>'.format(name, spec.origin)
            else:
                return '<module {!r} ({})>'.format(spec.name, spec.origin)

    def init_module_attrs(self, module, *, _override=False, _force_name=True):
        """Set the module's attributes.

        All missing import-related module attributes will be set.  Here
        is how the spec attributes map onto the module:

        spec.name -> module.__name__
        spec.loader -> module.__loader__
        spec.parent -> module.__package__
        spec -> module.__spec__

        Optional:
        spec.origin -> module.__file__ (if spec.set_fileattr is true)
        spec.cached -> module.__cached__ (if __file__ also set)
        spec.submodule_search_locations -> module.__path__ (if set)

        """
        spec = self.spec

        # The passed in module may be not support attribute assignment,
        # in which case we simply don't set the attributes.

        # __name__
        if (_override or _force_name or
            getattr(module, '__name__', None) is None):
            try:
                module.__name__ = spec.name
            except AttributeError:
                pass

        # __loader__
        if _override or getattr(module, '__loader__', None) is None:
            loader = spec.loader
            if loader is None:
                # A backward compatibility hack.
                if spec.submodule_search_locations is not None:
                    loader = _NamespaceLoader.__new__(_NamespaceLoader)
                    loader._path = spec.submodule_search_locations
            try:
                module.__loader__ = loader
            except AttributeError:
                pass

        # __package__
        if _override or getattr(module, '__package__', None) is None:
            try:
                module.__package__ = spec.parent
            except AttributeError:
                pass

        # __spec__
        try:
            module.__spec__ = spec
        except AttributeError:
            pass

        # __path__
        if _override or getattr(module, '__path__', None) is None:
            if spec.submodule_search_locations is not None:
                try:
                    module.__path__ = spec.submodule_search_locations
                except AttributeError:
                    pass

        if spec.has_location:
            # __file__
            if _override or getattr(module, '__file__', None) is None:
                try:
                    module.__file__ = spec.origin
                except AttributeError:
                    pass

            # __cached__
            if _override or getattr(module, '__cached__', None) is None:
                if spec.cached is not None:
                    try:
                        module.__cached__ = spec.cached
                    except AttributeError:
                        pass

    def create(self):
        """Return a new module to be loaded.

        The import-related module attributes are also set with the
        appropriate values from the spec.

        """
        spec = self.spec
        # Typically loaders will not implement create_module().
        if hasattr(spec.loader, 'create_module'):
            # If create_module() returns `None` it means the default
            # module creation should be used.
            module = spec.loader.create_module(spec)
        else:
            module = None
        if module is None:
            # This must be done before open() is ever called as the 'io'
            # module implicitly imports 'locale' and would otherwise
            # trigger an infinite loop.
            module = _new_module(spec.name)
        self.init_module_attrs(module)
        return module

    def _exec(self, module):
        """Do everything necessary to execute the module.

        The namespace of `module` is used as the target of execution.
        This method uses the loader's `exec_module()` method.

        """
        self.spec.loader.exec_module(module)

    # Used by importlib.reload() and _load_module_shim().
    def exec(self, module):
        """Execute the spec in an existing module's namespace."""
        name = self.spec.name
        _imp.acquire_lock()
        with _ModuleLockManager(name):
            if sys.modules.get(name) is not module:
                msg = 'module {!r} not in sys.modules'.format(name)
                raise ImportError(msg, name=name)
            if self.spec.loader is None:
                if self.spec.submodule_search_locations is None:
                    raise ImportError('missing loader', name=self.spec.name)
                # namespace package
                self.init_module_attrs(module, _override=True)
                return module
            self.init_module_attrs(module, _override=True)
            if not hasattr(self.spec.loader, 'exec_module'):
                # (issue19713) Once BuiltinImporter and ExtensionFileLoader
                # have exec_module() implemented, we can add a deprecation
                # warning here.
                self.spec.loader.load_module(name)
            else:
                self._exec(module)
        return sys.modules[name]

    def _load_backward_compatible(self):
        # (issue19713) Once BuiltinImporter and ExtensionFileLoader
        # have exec_module() implemented, we can add a deprecation
        # warning here.
        spec = self.spec
        spec.loader.load_module(spec.name)
        # The module must be in sys.modules at this point!
        module = sys.modules[spec.name]
        if getattr(module, '__loader__', None) is None:
            try:
                module.__loader__ = spec.loader
            except AttributeError:
                pass
        if getattr(module, '__package__', None) is None:
            try:
                # Since module.__path__ may not line up with
                # spec.submodule_search_paths, we can't necessarily rely
                # on spec.parent here.
                module.__package__ = module.__name__
                if not hasattr(module, '__path__'):
                    module.__package__ = spec.name.rpartition('.')[0]
            except AttributeError:
                pass
        if getattr(module, '__spec__', None) is None:
            try:
                module.__spec__ = spec
            except AttributeError:
                pass
        return module

    def _load_unlocked(self):
        # A helper for direct use by the import system.
        if self.spec.loader is not None:
            # not a namespace package
            if not hasattr(self.spec.loader, 'exec_module'):
                return self._load_backward_compatible()

        module = self.create()
        with _installed_safely(module):
            if self.spec.loader is None:
                if self.spec.submodule_search_locations is None:
                    raise ImportError('missing loader', name=self.spec.name)
                # A namespace package so do nothing.
            else:
                self._exec(module)

        # We don't ensure that the import-related module attributes get
        # set in the sys.modules replacement case.  Such modules are on
        # their own.
        return sys.modules[self.spec.name]

    # A method used during testing of _load_unlocked() and by
    # _load_module_shim().
    def load(self):
        """Return a new module object, loaded by the spec's loader.

        The module is not added to its parent.

        If a module is already in sys.modules, that existing module gets
        clobbered.

        """
        _imp.acquire_lock()
        with _ModuleLockManager(self.spec.name):
            return self._load_unlocked()


def _fix_up_module(ns, name, pathname, cpathname=None):
    # This function is used by PyImport_ExecCodeModuleObject().
    loader = ns.get('__loader__')
    spec = ns.get('__spec__')
    if not loader:
        if spec:
            loader = spec.loader
        elif pathname == cpathname:
            loader = SourcelessFileLoader(name, pathname)
        else:
            loader = SourceFileLoader(name, pathname)
    if not spec:
        spec = spec_from_file_location(name, pathname, loader=loader)
    try:
        ns['__spec__'] = spec
        ns['__loader__'] = loader
        ns['__file__'] = pathname
        ns['__cached__'] = cpathname
    except Exception:
        # Not important enough to report.
        pass


# Loaders #####################################################################

class BuiltinImporter:

    """Meta path import for built-in modules.

    All methods are either class or static methods to avoid the need to
    instantiate the class.

    """

    @staticmethod
    def module_repr(module):
        """Return repr for the module.

        The method is deprecated.  The import machinery does the job itself.

        """
        return '<module {!r} (built-in)>'.format(module.__name__)

    @classmethod
    def find_spec(cls, fullname, path=None, target=None):
        if path is not None:
            return None
        if _imp.is_builtin(fullname):
            return spec_from_loader(fullname, cls, origin='built-in')
        else:
            return None

    @classmethod
    def find_module(cls, fullname, path=None):
        """Find the built-in module.

        If 'path' is ever specified then the search is considered a failure.

        This method is deprecated.  Use find_spec() instead.

        """
        spec = cls.find_spec(fullname, path)
        return spec.loader if spec is not None else None

    @classmethod
    @_requires_builtin
    def load_module(cls, fullname):
        """Load a built-in module."""
        # Once an exec_module() implementation is added we can also
        # add a deprecation warning here.
        with _ManageReload(fullname):
            module = _call_with_frames_removed(_imp.init_builtin, fullname)
        module.__loader__ = cls
        module.__package__ = ''
        return module

    @classmethod
    @_requires_builtin
    def get_code(cls, fullname):
        """Return None as built-in modules do not have code objects."""
        return None

    @classmethod
    @_requires_builtin
    def get_source(cls, fullname):
        """Return None as built-in modules do not have source code."""
        return None

    @classmethod
    @_requires_builtin
    def is_package(cls, fullname):
        """Return False as built-in modules are never packages."""
        return False


class FrozenImporter:

    """Meta path import for frozen modules.

    All methods are either class or static methods to avoid the need to
    instantiate the class.

    """

    @staticmethod
    def module_repr(m):
        """Return repr for the module.

        The method is deprecated.  The import machinery does the job itself.

        """
        return '<module {!r} (frozen)>'.format(m.__name__)

    @classmethod
    def find_spec(cls, fullname, path=None, target=None):
        if _imp.is_frozen(fullname):
            return spec_from_loader(fullname, cls, origin='frozen')
        else:
            return None

    @classmethod
    def find_module(cls, fullname, path=None):
        """Find a frozen module.

        This method is deprecated.  Use find_spec() instead.

        """
        return cls if _imp.is_frozen(fullname) else None

    @staticmethod
    def exec_module(module):
        name = module.__spec__.name
        if not _imp.is_frozen(name):
            raise ImportError('{!r} is not a frozen module'.format(name),
                              name=name)
        code = _call_with_frames_removed(_imp.get_frozen_object, name)
        exec(code, module.__dict__)

    @classmethod
    def load_module(cls, fullname):
        """Load a frozen module.

        This method is deprecated.  Use exec_module() instead.

        """
        return _load_module_shim(cls, fullname)

    @classmethod
    @_requires_frozen
    def get_code(cls, fullname):
        """Return the code object for the frozen module."""
        return _imp.get_frozen_object(fullname)

    @classmethod
    @_requires_frozen
    def get_source(cls, fullname):
        """Return None as frozen modules do not have source code."""
        return None

    @classmethod
    @_requires_frozen
    def is_package(cls, fullname):
        """Return True if the frozen module is a package."""
        return _imp.is_frozen_package(fullname)


class WindowsRegistryFinder:

    """Meta path finder for modules declared in the Windows registry."""

    REGISTRY_KEY = (
        'Software\\Python\\PythonCore\\{sys_version}'
        '\\Modules\\{fullname}')
    REGISTRY_KEY_DEBUG = (
        'Software\\Python\\PythonCore\\{sys_version}'
        '\\Modules\\{fullname}\\Debug')
    DEBUG_BUILD = False  # Changed in _setup()

    @classmethod
    def _open_registry(cls, key):
        try:
            return _winreg.OpenKey(_winreg.HKEY_CURRENT_USER, key)
        except OSError:
            return _winreg.OpenKey(_winreg.HKEY_LOCAL_MACHINE, key)

    @classmethod
    def _search_registry(cls, fullname):
        if cls.DEBUG_BUILD:
            registry_key = cls.REGISTRY_KEY_DEBUG
        else:
            registry_key = cls.REGISTRY_KEY
        key = registry_key.format(fullname=fullname,
                                  sys_version=sys.version[:3])
        try:
            with cls._open_registry(key) as hkey:
                filepath = _winreg.QueryValue(hkey, '')
        except OSError:
            return None
        return filepath

    @classmethod
    def find_spec(cls, fullname, path=None, target=None):
        filepath = cls._search_registry(fullname)
        if filepath is None:
            return None
        try:
            _path_stat(filepath)
        except OSError:
            return None
        for loader, suffixes in _get_supported_file_loaders():
            if filepath.endswith(tuple(suffixes)):
                spec = spec_from_loader(fullname, loader(fullname, filepath),
                                        origin=filepath)
                return spec

    @classmethod
    def find_module(cls, fullname, path=None):
        """Find module named in the registry.

        This method is deprecated.  Use exec_module() instead.

        """
        spec = cls.find_spec(fullname, path)
        if spec is not None:
            return spec.loader
        else:
            return None


class _LoaderBasics:

    """Base class of common code needed by both SourceLoader and
    SourcelessFileLoader."""

    def is_package(self, fullname):
        """Concrete implementation of InspectLoader.is_package by checking if
        the path returned by get_filename has a filename of '__init__.py'."""
        filename = _path_split(self.get_filename(fullname))[1]
        filename_base = filename.rsplit('.', 1)[0]
        tail_name = fullname.rpartition('.')[2]
        return filename_base == '__init__' and tail_name != '__init__'

    def exec_module(self, module):
        """Execute the module."""
        code = self.get_code(module.__name__)
        if code is None:
            raise ImportError('cannot load module {!r} when get_code() '
                              'returns None'.format(module.__name__))
        _call_with_frames_removed(exec, code, module.__dict__)

    load_module = _load_module_shim


class SourceLoader(_LoaderBasics):

    def path_mtime(self, path):
        """Optional method that returns the modification time (an int) for the
        specified path, where path is a str.

        Raises IOError when the path cannot be handled.
        """
        raise IOError

    def path_stats(self, path):
        """Optional method returning a metadata dict for the specified path
        to by the path (str).
        Possible keys:
        - 'mtime' (mandatory) is the numeric timestamp of last source
          code modification;
        - 'size' (optional) is the size in bytes of the source code.

        Implementing this method allows the loader to read bytecode files.
        Raises IOError when the path cannot be handled.
        """
        return {'mtime': self.path_mtime(path)}

    def _cache_bytecode(self, source_path, cache_path, data):
        """Optional method which writes data (bytes) to a file path (a str).

        Implementing this method allows for the writing of bytecode files.

        The source path is needed in order to correctly transfer permissions
        """
        # For backwards compatibility, we delegate to set_data()
        return self.set_data(cache_path, data)

    def set_data(self, path, data):
        """Optional method which writes data (bytes) to a file path (a str).

        Implementing this method allows for the writing of bytecode files.
        """


    def get_source(self, fullname):
        """Concrete implementation of InspectLoader.get_source."""
        path = self.get_filename(fullname)
        try:
            source_bytes = self.get_data(path)
        except OSError as exc:
            raise ImportError('source not available through get_data()',
                              name=fullname) from exc
        return decode_source(source_bytes)

    def source_to_code(self, data, path, *, _optimize=-1):
        """Return the code object compiled from source.

        The 'data' argument can be any object type that compile() supports.
        """
        return _call_with_frames_removed(compile, data, path, 'exec',
                                        dont_inherit=True, optimize=_optimize)

    def get_code(self, fullname):
        """Concrete implementation of InspectLoader.get_code.

        Reading of bytecode requires path_stats to be implemented. To write
        bytecode, set_data must also be implemented.

        """
        source_path = self.get_filename(fullname)
        source_mtime = None
        try:
            bytecode_path = cache_from_source(source_path)
        except NotImplementedError:
            bytecode_path = None
        else:
            try:
                st = self.path_stats(source_path)
            except IOError:
                pass
            else:
                source_mtime = int(st['mtime'])
                try:
                    data = self.get_data(bytecode_path)
                except OSError:
                    pass
                else:
                    try:
                        bytes_data = _validate_bytecode_header(data,
                                source_stats=st, name=fullname,
                                path=bytecode_path)
                    except (ImportError, EOFError):
                        pass
                    else:
                        _verbose_message('{} matches {}', bytecode_path,
                                        source_path)
                        return _compile_bytecode(bytes_data, name=fullname,
                                                 bytecode_path=bytecode_path,
                                                 source_path=source_path)
        source_bytes = self.get_data(source_path)
        code_object = self.source_to_code(source_bytes, source_path)
        _verbose_message('code object from {}', source_path)
        if (not sys.dont_write_bytecode and bytecode_path is not None and
                source_mtime is not None):
            data = _code_to_bytecode(code_object, source_mtime,
                    len(source_bytes))
            try:
                self._cache_bytecode(source_path, bytecode_path, data)
                _verbose_message('wrote {!r}', bytecode_path)
            except NotImplementedError:
                pass
        return code_object


class FileLoader:

    """Base file loader class which implements the loader protocol methods that
    require file system usage."""

    def __init__(self, fullname, path):
        """Cache the module name and the path to the file found by the
        finder."""
        self.name = fullname
        self.path = path

    def __eq__(self, other):
        return (self.__class__ == other.__class__ and
                self.__dict__ == other.__dict__)

    def __hash__(self):
        return hash(self.name) ^ hash(self.path)

    @_check_name
    def load_module(self, fullname):
        """Load a module from a file.

        This method is deprecated.  Use exec_module() instead.

        """
        # The only reason for this method is for the name check.
        # Issue #14857: Avoid the zero-argument form of super so the implementation
        # of that form can be updated without breaking the frozen module
        return super(FileLoader, self).load_module(fullname)

    @_check_name
    def get_filename(self, fullname):
        """Return the path to the source file as found by the finder."""
        return self.path

    def get_data(self, path):
        """Return the data from path as raw bytes."""
        with _io.FileIO(path, 'r') as file:
            return file.read()


class SourceFileLoader(FileLoader, SourceLoader):

    """Concrete implementation of SourceLoader using the file system."""

    def path_stats(self, path):
        """Return the metadata for the path."""
        st = _path_stat(path)
        return {'mtime': st.st_mtime, 'size': st.st_size}

    def _cache_bytecode(self, source_path, bytecode_path, data):
        # Adapt between the two APIs
        mode = _calc_mode(source_path)
        return self.set_data(bytecode_path, data, _mode=mode)

    def set_data(self, path, data, *, _mode=0o666):
        """Write bytes data to a file."""
        parent, filename = _path_split(path)
        path_parts = []
        # Figure out what directories are missing.
        while parent and not _path_isdir(parent):
            parent, part = _path_split(parent)
            path_parts.append(part)
        # Create needed directories.
        for part in reversed(path_parts):
            parent = _path_join(parent, part)
            try:
                _os.mkdir(parent)
            except FileExistsError:
                # Probably another Python process already created the dir.
                continue
            except OSError as exc:
                # Could be a permission error, read-only filesystem: just forget
                # about writing the data.
                _verbose_message('could not create {!r}: {!r}', parent, exc)
                return
        try:
            _write_atomic(path, data, _mode)
            _verbose_message('created {!r}', path)
        except OSError as exc:
            # Same as above: just don't write the bytecode.
            _verbose_message('could not create {!r}: {!r}', path, exc)


class SourcelessFileLoader(FileLoader, _LoaderBasics):

    """Loader which handles sourceless file imports."""

    def get_code(self, fullname):
        path = self.get_filename(fullname)
        data = self.get_data(path)
        bytes_data = _validate_bytecode_header(data, name=fullname, path=path)
        return _compile_bytecode(bytes_data, name=fullname, bytecode_path=path)

    def get_source(self, fullname):
        """Return None as there is no source code."""
        return None


# Filled in by _setup().
EXTENSION_SUFFIXES = []


class ExtensionFileLoader:

    """Loader for extension modules.

    The constructor is designed to work with FileFinder.

    """

    def __init__(self, name, path):
        self.name = name
        self.path = path

    def __eq__(self, other):
        return (self.__class__ == other.__class__ and
                self.__dict__ == other.__dict__)

    def __hash__(self):
        return hash(self.name) ^ hash(self.path)

    @_check_name
    def load_module(self, fullname):
        """Load an extension module."""
        # Once an exec_module() implementation is added we can also
        # add a deprecation warning here.
        with _ManageReload(fullname):
            module = _call_with_frames_removed(_imp.load_dynamic,
                                               fullname, self.path)
        _verbose_message('extension module loaded from {!r}', self.path)
        is_package = self.is_package(fullname)
        if is_package and not hasattr(module, '__path__'):
            module.__path__ = [_path_split(self.path)[0]]
        module.__loader__ = self
        module.__package__ = module.__name__
        if not is_package:
            module.__package__ = module.__package__.rpartition('.')[0]
        return module

    def is_package(self, fullname):
        """Return True if the extension module is a package."""
        file_name = _path_split(self.path)[1]
        return any(file_name == '__init__' + suffix
                   for suffix in EXTENSION_SUFFIXES)

    def get_code(self, fullname):
        """Return None as an extension module cannot create a code object."""
        return None

    def get_source(self, fullname):
        """Return None as extension modules have no source code."""
        return None

    @_check_name
    def get_filename(self, fullname):
        """Return the path to the source file as found by the finder."""
        return self.path


class _NamespacePath:
    """Represents a namespace package's path.  It uses the module name
    to find its parent module, and from there it looks up the parent's
    __path__.  When this changes, the module's own path is recomputed,
    using path_finder.  For top-level modules, the parent module's path
    is sys.path."""

    def __init__(self, name, path, path_finder):
        self._name = name
        self._path = path
        self._last_parent_path = tuple(self._get_parent_path())
        self._path_finder = path_finder

    def _find_parent_path_names(self):
        """Returns a tuple of (parent-module-name, parent-path-attr-name)"""
        parent, dot, me = self._name.rpartition('.')
        if dot == '':
            # This is a top-level module. sys.path contains the parent path.
            return 'sys', 'path'
        # Not a top-level module. parent-module.__path__ contains the
        #  parent path.
        return parent, '__path__'

    def _get_parent_path(self):
        parent_module_name, path_attr_name = self._find_parent_path_names()
        return getattr(sys.modules[parent_module_name], path_attr_name)

    def _recalculate(self):
        # If the parent's path has changed, recalculate _path
        parent_path = tuple(self._get_parent_path()) # Make a copy
        if parent_path != self._last_parent_path:
            spec = self._path_finder(self._name, parent_path)
            # Note that no changes are made if a loader is returned, but we
            #  do remember the new parent path
            if spec is not None and spec.loader is None:
                if spec.submodule_search_locations:
                    self._path = spec.submodule_search_locations
            self._last_parent_path = parent_path     # Save the copy
        return self._path

    def __iter__(self):
        return iter(self._recalculate())

    def __len__(self):
        return len(self._recalculate())

    def __repr__(self):
        return '_NamespacePath({!r})'.format(self._path)

    def __contains__(self, item):
        return item in self._recalculate()

    def append(self, item):
        self._path.append(item)


# We use this exclusively in init_module_attrs() for backward-compatibility.
class _NamespaceLoader:
    def __init__(self, name, path, path_finder):
        self._path = _NamespacePath(name, path, path_finder)

    @classmethod
    def module_repr(cls, module):
        """Return repr for the module.

        The method is deprecated.  The import machinery does the job itself.

        """
        return '<module {!r} (namespace)>'.format(module.__name__)

    def is_package(self, fullname):
        return True

    def get_source(self, fullname):
        return ''

    def get_code(self, fullname):
        return compile('', '<string>', 'exec', dont_inherit=True)

    def exec_module(self, module):
        pass

    def load_module(self, fullname):
        """Load a namespace module.

        This method is deprecated.  Use exec_module() instead.

        """
        # The import system never calls this method.
        _verbose_message('namespace module loaded with path {!r}', self._path)
        return _load_module_shim(self, fullname)


# Finders #####################################################################

class PathFinder:

    """Meta path finder for sys.path and package __path__ attributes."""

    @classmethod
    def invalidate_caches(cls):
        """Call the invalidate_caches() method on all path entry finders
        stored in sys.path_importer_caches (where implemented)."""
        for finder in sys.path_importer_cache.values():
            if hasattr(finder, 'invalidate_caches'):
                finder.invalidate_caches()

    @classmethod
    def _path_hooks(cls, path):
        """Search sequence of hooks for a finder for 'path'.

        If 'hooks' is false then use sys.path_hooks.

        """
        if not sys.path_hooks:
            _warnings.warn('sys.path_hooks is empty', ImportWarning)
        for hook in sys.path_hooks:
            try:
                return hook(path)
            except ImportError:
                continue
        else:
            return None

    @classmethod
    def _path_importer_cache(cls, path):
        """Get the finder for the path entry from sys.path_importer_cache.

        If the path entry is not in the cache, find the appropriate finder
        and cache it. If no finder is available, store None.

        """
        if path == '':
            path = _os.getcwd()
        try:
            finder = sys.path_importer_cache[path]
        except KeyError:
            finder = cls._path_hooks(path)
            sys.path_importer_cache[path] = finder
        return finder

    @classmethod
    def _legacy_get_spec(cls, fullname, finder):
        # This would be a good place for a DeprecationWarning if
        # we ended up going that route.
        if hasattr(finder, 'find_loader'):
            loader, portions = finder.find_loader(fullname)
        else:
            loader = finder.find_module(fullname)
            portions = []
        if loader is not None:
            return spec_from_loader(fullname, loader)
        spec = ModuleSpec(fullname, None)
        spec.submodule_search_locations = portions
        return spec

    @classmethod
    def _get_spec(cls, fullname, path, target=None):
        """Find the loader or namespace_path for this module/package name."""
        # If this ends up being a namespace package, namespace_path is
        #  the list of paths that will become its __path__
        namespace_path = []
        for entry in path:
            if not isinstance(entry, (str, bytes)):
                continue
            finder = cls._path_importer_cache(entry)
            if finder is not None:
                if hasattr(finder, 'find_spec'):
                    spec = finder.find_spec(fullname, target)
                else:
                    spec = cls._legacy_get_spec(fullname, finder)
                if spec is None:
                    continue
                if spec.loader is not None:
                    return spec
                portions = spec.submodule_search_locations
                if portions is None:
                    raise ImportError('spec missing loader')
                # This is possibly part of a namespace package.
                #  Remember these path entries (if any) for when we
                #  create a namespace package, and continue iterating
                #  on path.
                namespace_path.extend(portions)
        else:
            spec = ModuleSpec(fullname, None)
            spec.submodule_search_locations = namespace_path
            return spec

    @classmethod
    def find_spec(cls, fullname, path=None, target=None):
        """find the module on sys.path or 'path' based on sys.path_hooks and
        sys.path_importer_cache."""
        if path is None:
            path = sys.path
        spec = cls._get_spec(fullname, path, target)
        if spec is None:
            return None
        elif spec.loader is None:
            namespace_path = spec.submodule_search_locations
            if namespace_path:
                # We found at least one namespace path.  Return a
                #  spec which can create the namespace package.
                spec.origin = 'namespace'
                spec.submodule_search_locations = _NamespacePath(fullname, namespace_path, cls._get_spec)
                return spec
            else:
                return None
        else:
            return spec

    @classmethod
    def find_module(cls, fullname, path=None):
        """find the module on sys.path or 'path' based on sys.path_hooks and
        sys.path_importer_cache.

        This method is deprecated.  Use find_spec() instead.

        """
        spec = cls.find_spec(fullname, path)
        if spec is None:
            return None
        return spec.loader


class FileFinder:

    """File-based finder.

    Interactions with the file system are cached for performance, being
    refreshed when the directory the finder is handling has been modified.

    """

    def __init__(self, path, *loader_details):
        """Initialize with the path to search on and a variable number of
        2-tuples containing the loader and the file suffixes the loader
        recognizes."""
        loaders = []
        for loader, suffixes in loader_details:
            loaders.extend((suffix, loader) for suffix in suffixes)
        self._loaders = loaders
        # Base (directory) path
        self.path = path or '.'
        self._path_mtime = -1
        self._path_cache = set()
        self._relaxed_path_cache = set()

    def invalidate_caches(self):
        """Invalidate the directory mtime."""
        self._path_mtime = -1

    find_module = _find_module_shim

    def find_loader(self, fullname):
        """Try to find a loader for the specified module, or the namespace
        package portions. Returns (loader, list-of-portions).

        This method is deprecated.  Use find_spec() instead.

        """
        spec = self.find_spec(fullname)
        if spec is None:
            return None, []
        return spec.loader, spec.submodule_search_locations or []

    def _get_spec(self, loader_class, fullname, path, smsl, target):
        loader = loader_class(fullname, path)
        return spec_from_file_location(fullname, path, loader=loader,
                                       submodule_search_locations=smsl)

    def find_spec(self, fullname, target=None):
        """Try to find a loader for the specified module, or the namespace
        package portions. Returns (loader, list-of-portions)."""
        is_namespace = False
        tail_module = fullname.rpartition('.')[2]
        try:
            mtime = _path_stat(self.path or _os.getcwd()).st_mtime
        except OSError:
            mtime = -1
        if mtime != self._path_mtime:
            self._fill_cache()
            self._path_mtime = mtime
        # tail_module keeps the original casing, for __file__ and friends
        if _relax_case():
            cache = self._relaxed_path_cache
            cache_module = tail_module.lower()
        else:
            cache = self._path_cache
            cache_module = tail_module
        # Check if the module is the name of a directory (and thus a package).
        if cache_module in cache:
            base_path = _path_join(self.path, tail_module)
            for suffix, loader_class in self._loaders:
                init_filename = '__init__' + suffix
                full_path = _path_join(base_path, init_filename)
                if _path_isfile(full_path):
                    return self._get_spec(loader_class, fullname, full_path, [base_path], target)
            else:
                # If a namespace package, return the path if we don't
                #  find a module in the next section.
                is_namespace = _path_isdir(base_path)
        # Check for a file w/ a proper suffix exists.
        for suffix, loader_class in self._loaders:
            full_path = _path_join(self.path, tail_module + suffix)
            _verbose_message('trying {}'.format(full_path), verbosity=2)
            if cache_module + suffix in cache:
                if _path_isfile(full_path):
                    return self._get_spec(loader_class, fullname, full_path, None, target)
        if is_namespace:
            _verbose_message('possible namespace for {}'.format(base_path))
            spec = ModuleSpec(fullname, None)
            spec.submodule_search_locations = [base_path]
            return spec
        return None

    def _fill_cache(self):
        """Fill the cache of potential modules and packages for this directory."""
        path = self.path
        try:
            contents = _os.listdir(path or _os.getcwd())
        except (FileNotFoundError, PermissionError, NotADirectoryError):
            # Directory has either been removed, turned into a file, or made
            # unreadable.
            contents = []
        # We store two cached versions, to handle runtime changes of the
        # PYTHONCASEOK environment variable.
        if not sys.platform.startswith('win'):
            self._path_cache = set(contents)
        else:
            # Windows users can import modules with case-insensitive file
            # suffixes (for legacy reasons). Make the suffix lowercase here
            # so it's done once instead of for every import. This is safe as
            # the specified suffixes to check against are always specified in a
            # case-sensitive manner.
            lower_suffix_contents = set()
            for item in contents:
                name, dot, suffix = item.partition('.')
                if dot:
                    new_name = '{}.{}'.format(name, suffix.lower())
                else:
                    new_name = name
                lower_suffix_contents.add(new_name)
            self._path_cache = lower_suffix_contents
        if sys.platform.startswith(_CASE_INSENSITIVE_PLATFORMS):
            self._relaxed_path_cache = {fn.lower() for fn in contents}

    @classmethod
    def path_hook(cls, *loader_details):
        """A class method which returns a closure to use on sys.path_hook
        which will return an instance using the specified loaders and the path
        called on the closure.

        If the path called on the closure is not a directory, ImportError is
        raised.

        """
        def path_hook_for_FileFinder(path):
            """Path hook for importlib.machinery.FileFinder."""
            if not _path_isdir(path):
                raise ImportError('only directories are supported', path=path)
            return cls(path, *loader_details)

        return path_hook_for_FileFinder

    def __repr__(self):
        return 'FileFinder({!r})'.format(self.path)


# Import itself ###############################################################

class _ImportLockContext:

    """Context manager for the import lock."""

    def __enter__(self):
        """Acquire the import lock."""
        _imp.acquire_lock()

    def __exit__(self, exc_type, exc_value, exc_traceback):
        """Release the import lock regardless of any raised exceptions."""
        _imp.release_lock()


def _resolve_name(name, package, level):
    """Resolve a relative module name to an absolute one."""
    bits = package.rsplit('.', level - 1)
    if len(bits) < level:
        raise ValueError('attempted relative import beyond top-level package')
    base = bits[0]
    return '{}.{}'.format(base, name) if name else base


def _find_spec_legacy(finder, name, path):
    # This would be a good place for a DeprecationWarning if
    # we ended up going that route.
    loader = finder.find_module(name, path)
    if loader is None:
        return None
    return spec_from_loader(name, loader)


def _find_spec(name, path, target=None):
    """Find a module's loader."""
    if not sys.meta_path:
        _warnings.warn('sys.meta_path is empty', ImportWarning)
    # We check sys.modules here for the reload case.  While a passed-in
    # target will usually indicate a reload there is no guarantee, whereas
    # sys.modules provides one.
    is_reload = name in sys.modules
    for finder in sys.meta_path:
        with _ImportLockContext():
            try:
                find_spec = finder.find_spec
            except AttributeError:
                spec = _find_spec_legacy(finder, name, path)
                if spec is None:
                    continue
            else:
                spec = find_spec(name, path, target)
        if spec is not None:
            # The parent import may have already imported this module.
            if not is_reload and name in sys.modules:
                module = sys.modules[name]
                try:
                    __spec__ = module.__spec__
                except AttributeError:
                    # We use the found spec since that is the one that
                    # we would have used if the parent module hadn't
                    # beaten us to the punch.
                    return spec
                else:
                    if __spec__ is None:
                        return spec
                    else:
                        return __spec__
            else:
                return spec
    else:
        return None


def _sanity_check(name, package, level):
    """Verify arguments are "sane"."""
    if not isinstance(name, str):
        raise TypeError('module name must be str, not {}'.format(type(name)))
    if level < 0:
        raise ValueError('level must be >= 0')
    if package:
        if not isinstance(package, str):
            raise TypeError('__package__ not set to a string')
        elif package not in sys.modules:
            msg = ('Parent module {!r} not loaded, cannot perform relative '
                   'import')
            raise SystemError(msg.format(package))
    if not name and level == 0:
        raise ValueError('Empty module name')


_ERR_MSG_PREFIX = 'No module named '
_ERR_MSG = _ERR_MSG_PREFIX + '{!r}'

def _find_and_load_unlocked(name, import_):
    path = None
    parent = name.rpartition('.')[0]
    if parent:
        if parent not in sys.modules:
            _call_with_frames_removed(import_, parent)
        # Crazy side-effects!
        if name in sys.modules:
            return sys.modules[name]
        parent_module = sys.modules[parent]
        try:
            path = parent_module.__path__
        except AttributeError:
            msg = (_ERR_MSG + '; {!r} is not a package').format(name, parent)
            raise ImportError(msg, name=name)
    spec = _find_spec(name, path)
    if spec is None:
        raise ImportError(_ERR_MSG.format(name), name=name)
    else:
        module = _SpecMethods(spec)._load_unlocked()
    if parent:
        # Set the module as an attribute on its parent.
        parent_module = sys.modules[parent]
        setattr(parent_module, name.rpartition('.')[2], module)
    return module


def _find_and_load(name, import_):
    """Find and load the module, and release the import lock."""
    with _ModuleLockManager(name):
        return _find_and_load_unlocked(name, import_)


def _gcd_import(name, package=None, level=0):
    """Import and return the module based on its name, the package the call is
    being made from, and the level adjustment.

    This function represents the greatest common denominator of functionality
    between import_module and __import__. This includes setting __package__ if
    the loader did not.

    """
    _sanity_check(name, package, level)
    if level > 0:
        name = _resolve_name(name, package, level)
    _imp.acquire_lock()
    if name not in sys.modules:
        return _find_and_load(name, _gcd_import)
    module = sys.modules[name]
    if module is None:
        _imp.release_lock()
        message = ('import of {} halted; '
                   'None in sys.modules'.format(name))
        raise ImportError(message, name=name)
    _lock_unlock_module(name)
    return module

def _handle_fromlist(module, fromlist, import_):
    """Figure out what __import__ should return.

    The import_ parameter is a callable which takes the name of module to
    import. It is required to decouple the function from assuming importlib's
    import implementation is desired.

    """
    # The hell that is fromlist ...
    # If a package was imported, try to import stuff from fromlist.
    if hasattr(module, '__path__'):
        if '*' in fromlist:
            fromlist = list(fromlist)
            fromlist.remove('*')
            if hasattr(module, '__all__'):
                fromlist.extend(module.__all__)
        for x in fromlist:
            if not hasattr(module, x):
                from_name = '{}.{}'.format(module.__name__, x)
                try:
                    _call_with_frames_removed(import_, from_name)
                except ImportError as exc:
                    # Backwards-compatibility dictates we ignore failed
                    # imports triggered by fromlist for modules that don't
                    # exist.
                    if str(exc).startswith(_ERR_MSG_PREFIX):
                        if exc.name == from_name:
                            continue
                    raise
    return module


def _calc___package__(globals):
    """Calculate what __package__ should be.

    __package__ is not guaranteed to be defined or could be set to None
    to represent that its proper value is unknown.

    """
    package = globals.get('__package__')
    if package is None:
        package = globals['__name__']
        if '__path__' not in globals:
            package = package.rpartition('.')[0]
    return package


def _get_supported_file_loaders():
    """Returns a list of file-based module loaders.

    Each item is a tuple (loader, suffixes).
    """
    extensions = ExtensionFileLoader, _imp.extension_suffixes()
    source = SourceFileLoader, SOURCE_SUFFIXES
    bytecode = SourcelessFileLoader, BYTECODE_SUFFIXES
    return [extensions, source, bytecode]


def __import__(name, globals=None, locals=None, fromlist=(), level=0):
    """Import a module.

    The 'globals' argument is used to infer where the import is occuring from
    to handle relative imports. The 'locals' argument is ignored. The
    'fromlist' argument specifies what should exist as attributes on the module
    being imported (e.g. ``from module import <fromlist>``).  The 'level'
    argument represents the package location to import from in a relative
    import (e.g. ``from ..pkg import mod`` would have a 'level' of 2).

    """
    if level == 0:
        module = _gcd_import(name)
    else:
        globals_ = globals if globals is not None else {}
        package = _calc___package__(globals_)
        module = _gcd_import(name, package, level)
    if not fromlist:
        # Return up to the first dot in 'name'. This is complicated by the fact
        # that 'name' may be relative.
        if level == 0:
            return _gcd_import(name.partition('.')[0])
        elif not name:
            return module
        else:
            # Figure out where to slice the module's name up to the first dot
            # in 'name'.
            cut_off = len(name) - len(name.partition('.')[0])
            # Slice end needs to be positive to alleviate need to special-case
            # when ``'.' not in name``.
            return sys.modules[module.__name__[:len(module.__name__)-cut_off]]
    else:
        return _handle_fromlist(module, fromlist, _gcd_import)


def _builtin_from_name(name):
    spec = BuiltinImporter.find_spec(name)
    if spec is None:
        raise ImportError('no built-in module named ' + name)
    methods = _SpecMethods(spec)
    return methods._load_unlocked()


def _setup(sys_module, _imp_module):
    """Setup importlib by importing needed built-in modules and injecting them
    into the global namespace.

    As sys is needed for sys.modules access and _imp is needed to load built-in
    modules, those two modules must be explicitly passed in.

    """
    global _imp, sys, BYTECODE_SUFFIXES
    _imp = _imp_module
    sys = sys_module

    if sys.flags.optimize:
        BYTECODE_SUFFIXES = OPTIMIZED_BYTECODE_SUFFIXES
    else:
        BYTECODE_SUFFIXES = DEBUG_BYTECODE_SUFFIXES

    # Set up the spec for existing builtin/frozen modules.
    module_type = type(sys)
    for name, module in sys.modules.items():
        if isinstance(module, module_type):
            if name in sys.builtin_module_names:
                loader = BuiltinImporter
            elif _imp.is_frozen(name):
                loader = FrozenImporter
            else:
                continue
            spec = _spec_from_module(module, loader)
            methods = _SpecMethods(spec)
            methods.init_module_attrs(module)

    # Directly load built-in modules needed during bootstrap.
    self_module = sys.modules[__name__]
    for builtin_name in ('_io', '_warnings', 'builtins', 'marshal'):
        if builtin_name not in sys.modules:
            builtin_module = _builtin_from_name(builtin_name)
        else:
            builtin_module = sys.modules[builtin_name]
        setattr(self_module, builtin_name, builtin_module)

    # Directly load the os module (needed during bootstrap).
    os_details = ('posix', ['/']), ('nt', ['\\', '/'])
    for builtin_os, path_separators in os_details:
        # Assumption made in _path_join()
        assert all(len(sep) == 1 for sep in path_separators)
        path_sep = path_separators[0]
        if builtin_os in sys.modules:
            os_module = sys.modules[builtin_os]
            break
        else:
            try:
                os_module = _builtin_from_name(builtin_os)
                break
            except ImportError:
                continue
    else:
        raise ImportError('importlib requires posix or nt')
    setattr(self_module, '_os', os_module)
    setattr(self_module, 'path_sep', path_sep)
    setattr(self_module, 'path_separators', ''.join(path_separators))

    # Directly load the _thread module (needed during bootstrap).
    try:
        thread_module = _builtin_from_name('_thread')
    except ImportError:
        # Python was built without threads
        thread_module = None
    setattr(self_module, '_thread', thread_module)

    # Directly load the _weakref module (needed during bootstrap).
    weakref_module = _builtin_from_name('_weakref')
    setattr(self_module, '_weakref', weakref_module)

    # Directly load the winreg module (needed during bootstrap).
    if builtin_os == 'nt':
        winreg_module = _builtin_from_name('winreg')
        setattr(self_module, '_winreg', winreg_module)

    # Constants
    setattr(self_module, '_relax_case', _make_relax_case())
    EXTENSION_SUFFIXES.extend(_imp.extension_suffixes())
    if builtin_os == 'nt':
        SOURCE_SUFFIXES.append('.pyw')
        if '_d.pyd' in EXTENSION_SUFFIXES:
            WindowsRegistryFinder.DEBUG_BUILD = True


def _install(sys_module, _imp_module):
    """Install importlib as the implementation of import."""
    _setup(sys_module, _imp_module)
    supported_loaders = _get_supported_file_loaders()
    sys.path_hooks.extend([FileFinder.path_hook(*supported_loaders)])
    sys.meta_path.append(BuiltinImporter)
    sys.meta_path.append(FrozenImporter)
    if _os.__name__ == 'nt':
        sys.meta_path.append(WindowsRegistryFinder)
    sys.meta_path.append(PathFinder)