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
|
:mod:`importlib` -- An implementation of :keyword:`import`
==========================================================
.. module:: importlib
:synopsis: An implementation of the import machinery.
.. moduleauthor:: Brett Cannon <brett@python.org>
.. sectionauthor:: Brett Cannon <brett@python.org>
.. versionadded:: 3.1
Introduction
------------
The purpose of the :mod:`importlib` package is two-fold. One is to provide an
implementation of the :keyword:`import` statement (and thus, by extension, the
:func:`__import__` function) in Python source code. This provides an
implementation of :keyword:`import` which is portable to any Python
interpreter. This also provides a reference implementation which is easier to
comprehend than one implemented in a programming language other than Python.
Two, the components to implement :keyword:`import` are exposed in this
package, making it easier for users to create their own custom objects (known
generically as an :term:`importer`) to participate in the import process.
Details on custom importers can be found in :pep:`302`.
.. seealso::
:ref:`import`
The language reference for the :keyword:`import` statement.
`Packages specification <http://www.python.org/doc/essays/packages.html>`__
Original specification of packages. Some semantics have changed since
the writing of this document (e.g. redirecting based on ``None``
in :data:`sys.modules`).
The :func:`.__import__` function
The :keyword:`import` statement is syntactic sugar for this function.
:pep:`235`
Import on Case-Insensitive Platforms
:pep:`263`
Defining Python Source Code Encodings
:pep:`302`
New Import Hooks
:pep:`328`
Imports: Multi-Line and Absolute/Relative
:pep:`366`
Main module explicit relative imports
:pep:`3120`
Using UTF-8 as the Default Source Encoding
:pep:`3147`
PYC Repository Directories
Functions
---------
.. function:: __import__(name, globals=None, locals=None, fromlist=(), level=0)
An implementation of the built-in :func:`__import__` function.
.. function:: import_module(name, package=None)
Import a module. The *name* argument specifies what module to
import in absolute or relative terms
(e.g. either ``pkg.mod`` or ``..mod``). If the name is
specified in relative terms, then the *package* argument must be set to
the name of the package which is to act as the anchor for resolving the
package name (e.g. ``import_module('..mod', 'pkg.subpkg')`` will import
``pkg.mod``).
The :func:`import_module` function acts as a simplifying wrapper around
:func:`importlib.__import__`. This means all semantics of the function are
derived from :func:`importlib.__import__`, including requiring the package
from which an import is occurring to have been previously imported
(i.e., *package* must already be imported). The most important difference
is that :func:`import_module` returns the most nested package or module
that was imported (e.g. ``pkg.mod``), while :func:`__import__` returns the
top-level package or module (e.g. ``pkg``).
.. function:: find_loader(name, path=None)
Find the loader for a module, optionally within the specified *path*. If the
module is in :attr:`sys.modules`, then ``sys.modules[name].__loader__`` is
returned (unless the loader would be ``None`` or is not set, in which case
:exc:`ValueError` is raised). Otherwise a search using :attr:`sys.meta_path`
is done. ``None`` is returned if no loader is found.
A dotted name does not have its parent's implicitly imported as that requires
loading them and that may not be desired. To properly import a submodule you
will need to import all parent packages of the submodule and use the correct
argument to *path*.
.. versionadded:: 3.3
.. versionchanged:: 3.4
If ``__loader__`` is not set, raise :exc:`ValueError`, just like when the
attribute is set to ``None``.
.. function:: invalidate_caches()
Invalidate the internal caches of finders stored at
:data:`sys.meta_path`. If a finder implements ``invalidate_caches()`` then it
will be called to perform the invalidation. This function should be called
if any modules are created/installed while your program is running to
guarantee all finders will notice the new module's existence.
.. versionadded:: 3.3
.. function:: reload(module)
Reload a previously imported *module*. The argument must be a module object,
so it must have been successfully imported before. This is useful if you
have edited the module source file using an external editor and want to try
out the new version without leaving the Python interpreter. The return value
is the module object (the same as the *module* argument).
When :func:`.reload` is executed:
* Python modules' code is recompiled and the module-level code re-executed,
defining a new set of objects which are bound to names in the module's
dictionary by reusing the :term:`loader` which originally loaded the
module. The ``init`` function of extension modules is not called a second
time.
* As with all other objects in Python the old objects are only reclaimed
after their reference counts drop to zero.
* The names in the module namespace are updated to point to any new or
changed objects.
* Other references to the old objects (such as names external to the module) are
not rebound to refer to the new objects and must be updated in each namespace
where they occur if that is desired.
There are a number of other caveats:
If a module is syntactically correct but its initialization fails, the first
:keyword:`import` statement for it does not bind its name locally, but does
store a (partially initialized) module object in ``sys.modules``. To reload
the module you must first :keyword:`import` it again (this will bind the name
to the partially initialized module object) before you can :func:`reload` it.
When a module is reloaded, its dictionary (containing the module's global
variables) is retained. Redefinitions of names will override the old
definitions, so this is generally not a problem. If the new version of a
module does not define a name that was defined by the old version, the old
definition remains. This feature can be used to the module's advantage if it
maintains a global table or cache of objects --- with a :keyword:`try`
statement it can test for the table's presence and skip its initialization if
desired::
try:
cache
except NameError:
cache = {}
It is legal though generally not very useful to reload built-in or
dynamically loaded modules (this is not true for e.g. :mod:`sys`,
:mod:`__main__`, :mod:`__builtin__` and other key modules where reloading is
frowned upon). In many cases, however, extension modules are not designed to
be initialized more than once, and may fail in arbitrary ways when reloaded.
If a module imports objects from another module using :keyword:`from` ...
:keyword:`import` ..., calling :func:`reload` for the other module does not
redefine the objects imported from it --- one way around this is to
re-execute the :keyword:`from` statement, another is to use :keyword:`import`
and qualified names (*module.name*) instead.
If a module instantiates instances of a class, reloading the module that
defines the class does not affect the method definitions of the instances ---
they continue to use the old class definition. The same is true for derived
classes.
.. versionadded:: 3.4
:mod:`importlib.abc` -- Abstract base classes related to import
---------------------------------------------------------------
.. module:: importlib.abc
:synopsis: Abstract base classes related to import
The :mod:`importlib.abc` module contains all of the core abstract base classes
used by :keyword:`import`. Some subclasses of the core abstract base classes
are also provided to help in implementing the core ABCs.
ABC hierarchy::
object
+-- Finder (deprecated)
| +-- MetaPathFinder
| +-- PathEntryFinder
+-- Loader
+-- ResourceLoader --------+
+-- InspectLoader |
+-- ExecutionLoader --+
+-- FileLoader
+-- SourceLoader
.. class:: Finder
An abstract base class representing a :term:`finder`.
.. deprecated:: 3.3
Use :class:`MetaPathFinder` or :class:`PathEntryFinder` instead.
.. method:: find_module(fullname, path=None)
An abstact method for finding a :term:`loader` for the specified
module. Originally specified in :pep:`302`, this method was meant
for use in :data:`sys.meta_path` and in the path-based import subsystem.
.. versionchanged:: 3.4
Returns ``None`` when called instead of raising
:exc:`NotImplementedError`.
.. class:: MetaPathFinder
An abstract base class representing a :term:`meta path finder`. For
compatibility, this is a subclass of :class:`Finder`.
.. versionadded:: 3.3
.. method:: find_module(fullname, path)
An abstract method for finding a :term:`loader` for the specified
module. If this is a top-level import, *path* will be ``None``.
Otherwise, this is a search for a subpackage or module and *path*
will be the value of :attr:`__path__` from the parent
package. If a loader cannot be found, ``None`` is returned.
.. versionchanged:: 3.4
Returns ``None`` when called instead of raising
:exc:`NotImplementedError`.
.. method:: invalidate_caches()
An optional method which, when called, should invalidate any internal
cache used by the finder. Used by :func:`importlib.invalidate_caches`
when invalidating the caches of all finders on :data:`sys.meta_path`.
.. versionchanged:: 3.4
Returns ``None`` when called instead of ``NotImplemented``.
.. class:: PathEntryFinder
An abstract base class representing a :term:`path entry finder`. Though
it bears some similarities to :class:`MetaPathFinder`, ``PathEntryFinder``
is meant for use only within the path-based import subsystem provided
by :class:`PathFinder`. This ABC is a subclass of :class:`Finder` for
compatibility reasons only.
.. versionadded:: 3.3
.. method:: find_loader(fullname)
An abstract method for finding a :term:`loader` for the specified
module. Returns a 2-tuple of ``(loader, portion)`` where ``portion``
is a sequence of file system locations contributing to part of a namespace
package. The loader may be ``None`` while specifying ``portion`` to
signify the contribution of the file system locations to a namespace
package. An empty list can be used for ``portion`` to signify the loader
is not part of a namespace package. If ``loader`` is ``None`` and
``portion`` is the empty list then no loader or location for a namespace
package were found (i.e. failure to find anything for the module).
.. versionchanged:: 3.4
Returns ``(None, [])`` instead of raising :exc:`NotImplementedError`.
.. method:: find_module(fullname)
A concrete implementation of :meth:`Finder.find_module` which is
equivalent to ``self.find_loader(fullname)[0]``.
.. method:: invalidate_caches()
An optional method which, when called, should invalidate any internal
cache used by the finder. Used by :meth:`PathFinder.invalidate_caches`
when invalidating the caches of all cached finders.
.. class:: Loader
An abstract base class for a :term:`loader`.
See :pep:`302` for the exact definition for a loader.
.. method:: load_module(fullname)
An abstract method for loading a module. If the module cannot be
loaded, :exc:`ImportError` is raised, otherwise the loaded module is
returned.
If the requested module already exists in :data:`sys.modules`, that
module should be used and reloaded.
Otherwise the loader should create a new module and insert it into
:data:`sys.modules` before any loading begins, to prevent recursion
from the import. If the loader inserted a module and the load fails, it
must be removed by the loader from :data:`sys.modules`; modules already
in :data:`sys.modules` before the loader began execution should be left
alone (see :func:`importlib.util.module_to_load`).
The loader should set several attributes on the module.
(Note that some of these attributes can change when a module is
reloaded; see :meth:`init_module_attrs`):
- :attr:`__name__`
The name of the module.
- :attr:`__file__`
The path to where the module data is stored (not set for built-in
modules).
- :attr:`__cached__`
The path to where a compiled version of the module is/should be
stored (not set when the attribute would be inappropriate).
- :attr:`__path__`
A list of strings specifying the search path within a
package. This attribute is not set on modules.
- :attr:`__package__`
The parent package for the module/package. If the module is
top-level then it has a value of the empty string. The
:func:`importlib.util.module_for_loader` decorator can handle the
details for :attr:`__package__`.
- :attr:`__loader__`
The loader used to load the module. The
:func:`importlib.util.module_for_loader` decorator can handle the
details for :attr:`__package__`.
.. versionchanged:: 3.4
Raise :exc:`ImportError` when called instead of
:exc:`NotImplementedError`.
.. method:: module_repr(module)
An optional method which when implemented calculates and returns the
given module's repr, as a string. The module type's default repr() will
use the result of this method as appropriate.
.. versionadded:: 3.3
.. versionchanged:: 3.4
Made optional instead of an abstractmethod.
.. method:: init_module_attrs(module)
Set the :attr:`__loader__` attribute on the module.
Subclasses overriding this method should set whatever appropriate
attributes it can, getting the module's name from :attr:`__name__` when
needed. All values should also be overridden so that reloading works as
expected.
.. versionadded:: 3.4
.. class:: ResourceLoader
An abstract base class for a :term:`loader` which implements the optional
:pep:`302` protocol for loading arbitrary resources from the storage
back-end.
.. method:: get_data(path)
An abstract method to return the bytes for the data located at *path*.
Loaders that have a file-like storage back-end
that allows storing arbitrary data
can implement this abstract method to give direct access
to the data stored. :exc:`IOError` is to be raised if the *path* cannot
be found. The *path* is expected to be constructed using a module's
:attr:`__file__` attribute or an item from a package's :attr:`__path__`.
.. versionchanged:: 3.4
Raises :exc:`IOError` instead of :exc:`NotImplementedError`.
.. class:: InspectLoader
An abstract base class for a :term:`loader` which implements the optional
:pep:`302` protocol for loaders that inspect modules.
.. method:: get_code(fullname)
Return the code object for a module.
``None`` should be returned if the module does not have a code object
(e.g. built-in module). :exc:`ImportError` is raised if loader cannot
find the requested module.
.. note::
While the method has a default implementation, it is suggested that
it be overridden if possible for performance.
.. index::
single: universal newlines; importlib.abc.InspectLoader.get_source method
.. versionchanged:: 3.4
No longer abstract and a concrete implementation is provided.
.. method:: get_source(fullname)
An abstract method to return the source of a module. It is returned as
a text string using :term:`universal newlines`, translating all
recognized line separators into ``'\n'`` characters. Returns ``None``
if no source is available (e.g. a built-in module). Raises
:exc:`ImportError` if the loader cannot find the module specified.
.. versionchanged:: 3.4
Raises :exc:`ImportError` instead of :exc:`NotImplementedError`.
.. method:: is_package(fullname)
An abstract method to return a true value if the module is a package, a
false value otherwise. :exc:`ImportError` is raised if the
:term:`loader` cannot find the module.
.. versionchanged:: 3.4
Raises :exc:`ImportError` instead of :exc:`NotImplementedError`.
.. method:: source_to_code(data, path='<string>')
Create a code object from Python source.
The *data* argument can be whatever the :func:`compile` function
supports (i.e. string or bytes). The *path* argument should be
the "path" to where the source code originated from, which can be an
abstract concept (e.g. location in a zip file).
.. versionadded:: 3.4
.. method:: init_module_attrs(module)
Set the :attr:`__package__` attribute and :attr:`__path__` attribute to
the empty list if appropriate along with what
:meth:`importlib.abc.Loader.init_module_attrs` sets.
.. versionadded:: 3.4
.. method:: load_module(fullname)
Implementation of :meth:`Loader.load_module`.
.. class:: ExecutionLoader
An abstract base class which inherits from :class:`InspectLoader` that,
when implemented, helps a module to be executed as a script. The ABC
represents an optional :pep:`302` protocol.
.. method:: get_filename(fullname)
An abstract method that is to return the value of :attr:`__file__` for
the specified module. If no path is available, :exc:`ImportError` is
raised.
If source code is available, then the method should return the path to
the source file, regardless of whether a bytecode was used to load the
module.
.. versionchanged:: 3.4
Raises :exc:`ImportError` instead of :exc:`NotImplementedError`.
.. method:: init_module_attrs(module)
Set :attr:`__file__` and if initializing a package then set
:attr:`__path__` to ``[os.path.dirname(__file__)]`` along with
all attributes set by
:meth:`importlib.abc.InspectLoader.init_module_attrs`.
.. versionadded:: 3.4
.. class:: FileLoader(fullname, path)
An abstract base class which inherits from :class:`ResourceLoader` and
:class:`ExecutionLoader`, providing concrete implementations of
:meth:`ResourceLoader.get_data` and :meth:`ExecutionLoader.get_filename`.
The *fullname* argument is a fully resolved name of the module the loader is
to handle. The *path* argument is the path to the file for the module.
.. versionadded:: 3.3
.. attribute:: name
The name of the module the loader can handle.
.. attribute:: path
Path to the file of the module.
.. method:: load_module(fullname)
Calls super's ``load_module()``.
.. method:: get_filename(fullname)
Returns :attr:`path`.
.. method:: get_data(path)
Reads *path* as a binary file and returns the bytes from it.
.. class:: SourceLoader
An abstract base class for implementing source (and optionally bytecode)
file loading. The class inherits from both :class:`ResourceLoader` and
:class:`ExecutionLoader`, requiring the implementation of:
* :meth:`ResourceLoader.get_data`
* :meth:`ExecutionLoader.get_filename`
Should only return the path to the source file; sourceless
loading is not supported.
The abstract methods defined by this class are to add optional bytecode
file support. Not implementing these optional methods (or causing them to
raise :exc:`NotImplementedError`) causes the loader to
only work with source code. Implementing the methods allows the loader to
work with source *and* bytecode files; it does not allow for *sourceless*
loading where only bytecode is provided. Bytecode files are an
optimization to speed up loading by removing the parsing step of Python's
compiler, and so no bytecode-specific API is exposed.
.. method:: path_stats(path)
Optional abstract method which returns a :class:`dict` containing
metadata about the specifed path. Supported dictionary keys are:
- ``'mtime'`` (mandatory): an integer or floating-point number
representing the modification time of the source code;
- ``'size'`` (optional): the size in bytes of the source code.
Any other keys in the dictionary are ignored, to allow for future
extensions. If the path cannot be handled, :exc:`IOError` is raised.
.. versionadded:: 3.3
.. versionchanged:: 3.4
Raise :exc:`IOError` instead of :exc:`NotImplementedError`.
.. method:: path_mtime(path)
Optional abstract method which returns the modification time for the
specified path.
.. deprecated:: 3.3
This method is deprecated in favour of :meth:`path_stats`. You don't
have to implement it, but it is still available for compatibility
purposes. Raise :exc:`IOError` if the path cannot be handled.
.. versionchanged:: 3.4
Raise :exc:`IOError` instead of :exc:`NotImplementedError`.
.. method:: set_data(path, data)
Optional abstract method which writes the specified bytes to a file
path. Any intermediate directories which do not exist are to be created
automatically.
When writing to the path fails because the path is read-only
(:attr:`errno.EACCES`/:exc:`PermissionError`), do not propagate the
exception.
.. versionchanged:: 3.4
No longer raises :exc:`NotImplementedError` when called.
.. method:: get_code(fullname)
Concrete implementation of :meth:`InspectLoader.get_code`.
.. method:: load_module(fullname)
Concrete implementation of :meth:`Loader.load_module`.
.. method:: get_source(fullname)
Concrete implementation of :meth:`InspectLoader.get_source`.
.. method:: is_package(fullname)
Concrete implementation of :meth:`InspectLoader.is_package`. A module
is determined to be a package if its file path (as provided by
:meth:`ExecutionLoader.get_filename`) is a file named
``__init__`` when the file extension is removed **and** the module name
itself does not end in ``__init__``.
.. method:: init_module_attr(module)
Set :attr:`__cached__` using :func:`imp.cache_from_source`. Other
attributes set by
:meth:`importlib.abc.ExecutionLoader.init_module_attrs`.
.. versionadded:: 3.4
:mod:`importlib.machinery` -- Importers and path hooks
------------------------------------------------------
.. module:: importlib.machinery
:synopsis: Importers and path hooks
This module contains the various objects that help :keyword:`import`
find and load modules.
.. attribute:: SOURCE_SUFFIXES
A list of strings representing the recognized file suffixes for source
modules.
.. versionadded:: 3.3
.. attribute:: DEBUG_BYTECODE_SUFFIXES
A list of strings representing the file suffixes for non-optimized bytecode
modules.
.. versionadded:: 3.3
.. attribute:: OPTIMIZED_BYTECODE_SUFFIXES
A list of strings representing the file suffixes for optimized bytecode
modules.
.. versionadded:: 3.3
.. attribute:: BYTECODE_SUFFIXES
A list of strings representing the recognized file suffixes for bytecode
modules. Set to either :attr:`DEBUG_BYTECODE_SUFFIXES` or
:attr:`OPTIMIZED_BYTECODE_SUFFIXES` based on whether ``__debug__`` is true.
.. versionadded:: 3.3
.. attribute:: EXTENSION_SUFFIXES
A list of strings representing the recognized file suffixes for
extension modules.
.. versionadded:: 3.3
.. function:: all_suffixes()
Returns a combined list of strings representing all file suffixes for
modules recognized by the standard import machinery. This is a
helper for code which simply needs to know if a filesystem path
potentially refers to a module without needing any details on the kind
of module (for example, :func:`inspect.getmodulename`)
.. versionadded:: 3.3
.. class:: BuiltinImporter
An :term:`importer` for built-in modules. All known built-in modules are
listed in :data:`sys.builtin_module_names`. This class implements the
:class:`importlib.abc.MetaPathFinder` and
:class:`importlib.abc.InspectLoader` ABCs.
Only class methods are defined by this class to alleviate the need for
instantiation.
.. class:: FrozenImporter
An :term:`importer` for frozen modules. This class implements the
:class:`importlib.abc.MetaPathFinder` and
:class:`importlib.abc.InspectLoader` ABCs.
Only class methods are defined by this class to alleviate the need for
instantiation.
.. class:: WindowsRegistryFinder
:term:`Finder` for modules declared in the Windows registry. This class
implements the :class:`importlib.abc.Finder` ABC.
Only class methods are defined by this class to alleviate the need for
instantiation.
.. versionadded:: 3.3
.. class:: PathFinder
A :term:`Finder` for :data:`sys.path` and package ``__path__`` attributes.
This class implements the :class:`importlib.abc.MetaPathFinder` ABC.
Only class methods are defined by this class to alleviate the need for
instantiation.
.. classmethod:: find_module(fullname, path=None)
Class method that attempts to find a :term:`loader` for the module
specified by *fullname* on :data:`sys.path` or, if defined, on
*path*. For each path entry that is searched,
:data:`sys.path_importer_cache` is checked. If a non-false object is
found then it is used as the :term:`path entry finder` to look for the
module being searched for. If no entry is found in
:data:`sys.path_importer_cache`, then :data:`sys.path_hooks` is
searched for a finder for the path entry and, if found, is stored in
:data:`sys.path_importer_cache` along with being queried about the
module. If no finder is ever found then ``None`` is both stored in
the cache and returned.
.. classmethod:: invalidate_caches()
Calls :meth:`importlib.abc.PathEntryFinder.invalidate_caches` on all
finders stored in :attr:`sys.path_importer_cache`.
.. class:: FileFinder(path, \*loader_details)
A concrete implementation of :class:`importlib.abc.PathEntryFinder` which
caches results from the file system.
The *path* argument is the directory for which the finder is in charge of
searching.
The *loader_details* argument is a variable number of 2-item tuples each
containing a loader and a sequence of file suffixes the loader recognizes.
The loaders are expected to be callables which accept two arguments of
the module's name and the path to the file found.
The finder will cache the directory contents as necessary, making stat calls
for each module search to verify the cache is not outdated. Because cache
staleness relies upon the granularity of the operating system's state
information of the file system, there is a potential race condition of
searching for a module, creating a new file, and then searching for the
module the new file represents. If the operations happen fast enough to fit
within the granularity of stat calls, then the module search will fail. To
prevent this from happening, when you create a module dynamically, make sure
to call :func:`importlib.invalidate_caches`.
.. versionadded:: 3.3
.. attribute:: path
The path the finder will search in.
.. method:: find_loader(fullname)
Attempt to find the loader to handle *fullname* within :attr:`path`.
.. method:: invalidate_caches()
Clear out the internal cache.
.. classmethod:: path_hook(\*loader_details)
A class method which returns a closure for use on :attr:`sys.path_hooks`.
An instance of :class:`FileFinder` is returned by the closure using the
path argument given to the closure directly and *loader_details*
indirectly.
If the argument to the closure is not an existing directory,
:exc:`ImportError` is raised.
.. class:: SourceFileLoader(fullname, path)
A concrete implementation of :class:`importlib.abc.SourceLoader` by
subclassing :class:`importlib.abc.FileLoader` and providing some concrete
implementations of other methods.
.. versionadded:: 3.3
.. attribute:: name
The name of the module that this loader will handle.
.. attribute:: path
The path to the source file.
.. method:: is_package(fullname)
Return true if :attr:`path` appears to be for a package.
.. method:: path_stats(path)
Concrete implementation of :meth:`importlib.abc.SourceLoader.path_stats`.
.. method:: set_data(path, data)
Concrete implementation of :meth:`importlib.abc.SourceLoader.set_data`.
.. class:: SourcelessFileLoader(fullname, path)
A concrete implementation of :class:`importlib.abc.FileLoader` which can
import bytecode files (i.e. no source code files exist).
Please note that direct use of bytecode files (and thus not source code
files) inhibits your modules from being usable by all Python
implementations or new versions of Python which change the bytecode
format.
.. versionadded:: 3.3
.. attribute:: name
The name of the module the loader will handle.
.. attribute:: path
The path to the bytecode file.
.. method:: is_package(fullname)
Determines if the module is a package based on :attr:`path`.
.. method:: get_code(fullname)
Returns the code object for :attr:`name` created from :attr:`path`.
.. method:: get_source(fullname)
Returns ``None`` as bytecode files have no source when this loader is
used.
.. class:: ExtensionFileLoader(fullname, path)
A concrete implementation of :class:`importlib.abc.InspectLoader` for
extension modules.
The *fullname* argument specifies the name of the module the loader is to
support. The *path* argument is the path to the extension module's file.
.. versionadded:: 3.3
.. attribute:: name
Name of the module the loader supports.
.. attribute:: path
Path to the extension module.
.. method:: load_module(fullname)
Loads the extension module if and only if *fullname* is the same as
:attr:`name` or is ``None``.
.. method:: is_package(fullname)
Returns ``True`` if the file path points to a package's ``__init__``
module based on :attr:`EXTENSION_SUFFIXES`.
.. method:: get_code(fullname)
Returns ``None`` as extension modules lack a code object.
.. method:: get_source(fullname)
Returns ``None`` as extension modules do not have source code.
:mod:`importlib.util` -- Utility code for importers
---------------------------------------------------
.. module:: importlib.util
:synopsis: Utility code for importers
This module contains the various objects that help in the construction of
an :term:`importer`.
.. attribute:: MAGIC_NUMBER
The bytes which represent the bytecode version number. If you need help with
loading/writing bytecode then consider :class:`importlib.abc.SourceLoader`.
.. versionadded:: 3.4
.. function:: cache_from_source(path, debug_override=None)
Return the :pep:`3147` path to the byte-compiled file associated with the
source *path*. For example, if *path* is ``/foo/bar/baz.py`` the return
value would be ``/foo/bar/__pycache__/baz.cpython-32.pyc`` for Python 3.2.
The ``cpython-32`` string comes from the current magic tag (see
:func:`get_tag`; if :attr:`sys.implementation.cache_tag` is not defined then
:exc:`NotImplementedError` will be raised). The returned path will end in
``.pyc`` when ``__debug__`` is True or ``.pyo`` for an optimized Python
(i.e. ``__debug__`` is False). By passing in True or False for
*debug_override* you can override the system's value for ``__debug__`` for
extension selection.
*path* need not exist.
.. versionadded:: 3.4
.. function:: source_from_cache(path)
Given the *path* to a :pep:`3147` file name, return the associated source code
file path. For example, if *path* is
``/foo/bar/__pycache__/baz.cpython-32.pyc`` the returned path would be
``/foo/bar/baz.py``. *path* need not exist, however if it does not conform
to :pep:`3147` format, a ``ValueError`` is raised. If
:attr:`sys.implementation.cache_tag` is not defined,
:exc:`NotImplementedError` is raised.
.. versionadded:: 3.4
.. function:: decode_source(source_bytes)
Decode the given bytes representing source code and return it as a string
with universal newlines (as required by
:meth:`importlib.abc.InspectLoader.get_source`).
.. versionadded:: 3.4
.. function:: resolve_name(name, package)
Resolve a relative module name to an absolute one.
If **name** has no leading dots, then **name** is simply returned. This
allows for usage such as
``importlib.util.resolve_name('sys', __package__)`` without doing a
check to see if the **package** argument is needed.
:exc:`ValueError` is raised if **name** is a relative module name but
package is a false value (e.g. ``None`` or the empty string).
:exc:`ValueError` is also raised a relative name would escape its containing
package (e.g. requesting ``..bacon`` from within the ``spam`` package).
.. versionadded:: 3.3
.. function:: module_to_load(name, *, reset_name=True)
Returns a :term:`context manager` which provides the module to load. The
module will either come from :attr:`sys.modules` in the case of reloading or
a fresh module if loading a new module. Proper cleanup of
:attr:`sys.modules` occurs if the module was new and an exception was
raised.
If **reset_name** is true and the module requested is being reloaded then
the module's :attr:`__name__` attribute will
be reset to **name**, else it will be left untouched.
.. versionadded:: 3.4
.. decorator:: module_for_loader
A :term:`decorator` for :meth:`importlib.abc.Loader.load_module`
to handle selecting the proper
module object to load with. The decorated method is expected to have a call
signature taking two positional arguments
(e.g. ``load_module(self, module)``) for which the second argument
will be the module **object** to be used by the loader.
Note that the decorator will not work on static methods because of the
assumption of two arguments.
The decorated method will take in the **name** of the module to be loaded
as expected for a :term:`loader`. If the module is not found in
:data:`sys.modules` then a new one is constructed. Regardless of where the
module came from, :attr:`__loader__` set to **self** and :attr:`__package__`
is set based on what :meth:`importlib.abc.InspectLoader.is_package` returns
(if available). These attributes are set unconditionally to support
reloading.
If an exception is raised by the decorated method and a module was added to
:data:`sys.modules`, then the module will be removed to prevent a partially
initialized module from being in left in :data:`sys.modules`. If the module
was already in :data:`sys.modules` then it is left alone.
.. versionchanged:: 3.3
:attr:`__loader__` and :attr:`__package__` are automatically set
(when possible).
.. versionchanged:: 3.4
Set :attr:`__name__`, :attr:`__loader__` :attr:`__package__`
unconditionally to support reloading.
.. deprecated:: 3.4
For the benefit of :term:`loader` subclasses, please use
:func:`module_to_load` and
:meth:`importlib.abc.Loader.init_module_attrs` instead.
.. decorator:: set_loader
A :term:`decorator` for :meth:`importlib.abc.Loader.load_module`
to set the :attr:`__loader__`
attribute on the returned module. If the attribute is already set the
decorator does nothing. It is assumed that the first positional argument to
the wrapped method (i.e. ``self``) is what :attr:`__loader__` should be set
to.
.. note::
As this decorator sets :attr:`__loader__` after loading the module, it is
recommended to use :meth:`importlib.abc.Loader.init_module_attrs` instead
when appropriate.
.. versionchanged:: 3.4
Set ``__loader__`` if set to ``None``, as if the attribute does not
exist.
.. decorator:: set_package
A :term:`decorator` for :meth:`importlib.abc.Loader.load_module` to set the :attr:`__package__` attribute on the returned module. If :attr:`__package__`
is set and has a value other than ``None`` it will not be changed.
.. note::
As this decorator sets :attr:`__package__` after loading the module, it is
recommended to use :meth:`importlib.abc.Loader.init_module_attrs` instead
when appropriate.
|