summaryrefslogtreecommitdiffstats
path: root/Lib/test/test_fstring.py
blob: 92995fd83e38d68ba4deca6c7e626445613c3cd4 (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
import ast
import types
import decimal
import unittest

a_global = 'global variable'

# You could argue that I'm too strict in looking for specific error
#  values with assertRaisesRegex, but without it it's way too easy to
#  make a syntax error in the test strings. Especially with all of the
#  triple quotes, raw strings, backslashes, etc. I think it's a
#  worthwhile tradeoff. When I switched to this method, I found many
#  examples where I wasn't testing what I thought I was.

class TestCase(unittest.TestCase):
    def assertAllRaise(self, exception_type, regex, error_strings):
        for str in error_strings:
            with self.subTest(str=str):
                with self.assertRaisesRegex(exception_type, regex):
                    eval(str)

    def test__format__lookup(self):
        # Make sure __format__ is looked up on the type, not the instance.
        class X:
            def __format__(self, spec):
                return 'class'

        x = X()

        # Add a bound __format__ method to the 'y' instance, but not
        #  the 'x' instance.
        y = X()
        y.__format__ = types.MethodType(lambda self, spec: 'instance', y)

        self.assertEqual(f'{y}', format(y))
        self.assertEqual(f'{y}', 'class')
        self.assertEqual(format(x), format(y))

        # __format__ is not called this way, but still make sure it
        #  returns what we expect (so we can make sure we're bypassing
        #  it).
        self.assertEqual(x.__format__(''), 'class')
        self.assertEqual(y.__format__(''), 'instance')

        # This is how __format__ is actually called.
        self.assertEqual(type(x).__format__(x, ''), 'class')
        self.assertEqual(type(y).__format__(y, ''), 'class')

    def test_ast(self):
        # Inspired by http://bugs.python.org/issue24975
        class X:
            def __init__(self):
                self.called = False
            def __call__(self):
                self.called = True
                return 4
        x = X()
        expr = """
a = 10
f'{a * x()}'"""
        t = ast.parse(expr)
        c = compile(t, '', 'exec')

        # Make sure x was not called.
        self.assertFalse(x.called)

        # Actually run the code.
        exec(c)

        # Make sure x was called.
        self.assertTrue(x.called)

    def test_literal_eval(self):
        # With no expressions, an f-string is okay.
        self.assertEqual(ast.literal_eval("f'x'"), 'x')
        self.assertEqual(ast.literal_eval("f'x' 'y'"), 'xy')

        # But this should raise an error.
        with self.assertRaisesRegex(ValueError, 'malformed node or string'):
            ast.literal_eval("f'x{3}'")

        # As should this, which uses a different ast node
        with self.assertRaisesRegex(ValueError, 'malformed node or string'):
            ast.literal_eval("f'{3}'")

    def test_ast_compile_time_concat(self):
        x = ['']

        expr = """x[0] = 'foo' f'{3}'"""
        t = ast.parse(expr)
        c = compile(t, '', 'exec')
        exec(c)
        self.assertEqual(x[0], 'foo3')

    def test_literal(self):
        self.assertEqual(f'', '')
        self.assertEqual(f'a', 'a')
        self.assertEqual(f' ', ' ')

    def test_unterminated_string(self):
        self.assertAllRaise(SyntaxError, 'f-string: unterminated string',
                            [r"""f'{"x'""",
                             r"""f'{"x}'""",
                             r"""f'{("x'""",
                             r"""f'{("x}'""",
                             ])

    def test_mismatched_parens(self):
        self.assertAllRaise(SyntaxError, 'f-string: mismatched',
                            ["f'{((}'",
                             ])

    def test_double_braces(self):
        self.assertEqual(f'{{', '{')
        self.assertEqual(f'a{{', 'a{')
        self.assertEqual(f'{{b', '{b')
        self.assertEqual(f'a{{b', 'a{b')
        self.assertEqual(f'}}', '}')
        self.assertEqual(f'a}}', 'a}')
        self.assertEqual(f'}}b', '}b')
        self.assertEqual(f'a}}b', 'a}b')
        self.assertEqual(f'{{}}', '{}')
        self.assertEqual(f'a{{}}', 'a{}')
        self.assertEqual(f'{{b}}', '{b}')
        self.assertEqual(f'{{}}c', '{}c')
        self.assertEqual(f'a{{b}}', 'a{b}')
        self.assertEqual(f'a{{}}c', 'a{}c')
        self.assertEqual(f'{{b}}c', '{b}c')
        self.assertEqual(f'a{{b}}c', 'a{b}c')

        self.assertEqual(f'{{{10}', '{10')
        self.assertEqual(f'}}{10}', '}10')
        self.assertEqual(f'}}{{{10}', '}{10')
        self.assertEqual(f'}}a{{{10}', '}a{10')

        self.assertEqual(f'{10}{{', '10{')
        self.assertEqual(f'{10}}}', '10}')
        self.assertEqual(f'{10}}}{{', '10}{')
        self.assertEqual(f'{10}}}a{{' '}', '10}a{}')

        # Inside of strings, don't interpret doubled brackets.
        self.assertEqual(f'{"{{}}"}', '{{}}')

        self.assertAllRaise(TypeError, 'unhashable type',
                            ["f'{ {{}} }'", # dict in a set
                             ])

    def test_compile_time_concat(self):
        x = 'def'
        self.assertEqual('abc' f'## {x}ghi', 'abc## defghi')
        self.assertEqual('abc' f'{x}' 'ghi', 'abcdefghi')
        self.assertEqual('abc' f'{x}' 'gh' f'i{x:4}', 'abcdefghidef ')
        self.assertEqual('{x}' f'{x}', '{x}def')
        self.assertEqual('{x' f'{x}', '{xdef')
        self.assertEqual('{x}' f'{x}', '{x}def')
        self.assertEqual('{{x}}' f'{x}', '{{x}}def')
        self.assertEqual('{{x' f'{x}', '{{xdef')
        self.assertEqual('x}}' f'{x}', 'x}}def')
        self.assertEqual(f'{x}' 'x}}', 'defx}}')
        self.assertEqual(f'{x}' '', 'def')
        self.assertEqual('' f'{x}' '', 'def')
        self.assertEqual('' f'{x}', 'def')
        self.assertEqual(f'{x}' '2', 'def2')
        self.assertEqual('1' f'{x}' '2', '1def2')
        self.assertEqual('1' f'{x}', '1def')
        self.assertEqual(f'{x}' f'-{x}', 'def-def')
        self.assertEqual('' f'', '')
        self.assertEqual('' f'' '', '')
        self.assertEqual('' f'' '' f'', '')
        self.assertEqual(f'', '')
        self.assertEqual(f'' '', '')
        self.assertEqual(f'' '' f'', '')
        self.assertEqual(f'' '' f'' '', '')

        self.assertAllRaise(SyntaxError, "f-string: expecting '}'",
                            ["f'{3' f'}'",  # can't concat to get a valid f-string
                             ])

    def test_comments(self):
        # These aren't comments, since they're in strings.
        d = {'#': 'hash'}
        self.assertEqual(f'{"#"}', '#')
        self.assertEqual(f'{d["#"]}', 'hash')

        self.assertAllRaise(SyntaxError, "f-string expression part cannot include '#'",
                            ["f'{1#}'",   # error because the expression becomes "(1#)"
                             "f'{3(#)}'",
                             "f'{#}'",
                             "f'{)#}'",   # When wrapped in parens, this becomes
                                          #  '()#)'.  Make sure that doesn't compile.
                             ])

    def test_many_expressions(self):
        # Create a string with many expressions in it. Note that
        #  because we have a space in here as a literal, we're actually
        #  going to use twice as many ast nodes: one for each literal
        #  plus one for each expression.
        def build_fstr(n, extra=''):
            return "f'" + ('{x} ' * n) + extra + "'"

        x = 'X'
        width = 1

        # Test around 256.
        for i in range(250, 260):
            self.assertEqual(eval(build_fstr(i)), (x+' ')*i)

        # Test concatenating 2 largs fstrings.
        self.assertEqual(eval(build_fstr(255)*256), (x+' ')*(255*256))

        s = build_fstr(253, '{x:{width}} ')
        self.assertEqual(eval(s), (x+' ')*254)

        # Test lots of expressions and constants, concatenated.
        s = "f'{1}' 'x' 'y'" * 1024
        self.assertEqual(eval(s), '1xy' * 1024)

    def test_format_specifier_expressions(self):
        width = 10
        precision = 4
        value = decimal.Decimal('12.34567')
        self.assertEqual(f'result: {value:{width}.{precision}}', 'result:      12.35')
        self.assertEqual(f'result: {value:{width!r}.{precision}}', 'result:      12.35')
        self.assertEqual(f'result: {value:{width:0}.{precision:1}}', 'result:      12.35')
        self.assertEqual(f'result: {value:{1}{0:0}.{precision:1}}', 'result:      12.35')
        self.assertEqual(f'result: {value:{ 1}{ 0:0}.{ precision:1}}', 'result:      12.35')
        self.assertEqual(f'{10:#{1}0x}', '       0xa')
        self.assertEqual(f'{10:{"#"}1{0}{"x"}}', '       0xa')
        self.assertEqual(f'{-10:-{"#"}1{0}x}', '      -0xa')
        self.assertEqual(f'{-10:{"-"}#{1}0{"x"}}', '      -0xa')
        self.assertEqual(f'{10:#{3 != {4:5} and width}x}', '       0xa')

        self.assertAllRaise(SyntaxError, "f-string: expecting '}'",
                            ["""f'{"s"!r{":10"}}'""",

                             # This looks like a nested format spec.
                             ])

        self.assertAllRaise(SyntaxError, "invalid syntax",
                            [# Invalid syntax inside a nested spec.
                             "f'{4:{/5}}'",
                             ])

        self.assertAllRaise(SyntaxError, "f-string: expressions nested too deeply",
                            [# Can't nest format specifiers.
                             "f'result: {value:{width:{0}}.{precision:1}}'",
                             ])

        self.assertAllRaise(SyntaxError, 'f-string: invalid conversion character',
                            [# No expansion inside conversion or for
                             #  the : or ! itself.
                             """f'{"s"!{"r"}}'""",
                             ])

    def test_side_effect_order(self):
        class X:
            def __init__(self):
                self.i = 0
            def __format__(self, spec):
                self.i += 1
                return str(self.i)

        x = X()
        self.assertEqual(f'{x} {x}', '1 2')

    def test_missing_expression(self):
        self.assertAllRaise(SyntaxError, 'f-string: empty expression not allowed',
                            ["f'{}'",
                             "f'{ }'"
                             "f' {} '",
                             "f'{!r}'",
                             "f'{ !r}'",
                             "f'{10:{ }}'",
                             "f' { } '",

                             # Catch the empty expression before the
                             #  invalid conversion.
                             "f'{!x}'",
                             "f'{ !xr}'",
                             "f'{!x:}'",
                             "f'{!x:a}'",
                             "f'{ !xr:}'",
                             "f'{ !xr:a}'",

                             "f'{!}'",
                             "f'{:}'",

                             # We find the empty expression before the
                             #  missing closing brace.
                             "f'{!'",
                             "f'{!s:'",
                             "f'{:'",
                             "f'{:x'",
                             ])

    def test_parens_in_expressions(self):
        self.assertEqual(f'{3,}', '(3,)')

        # Add these because when an expression is evaluated, parens
        #  are added around it. But we shouldn't go from an invalid
        #  expression to a valid one. The added parens are just
        #  supposed to allow whitespace (including newlines).
        self.assertAllRaise(SyntaxError, 'invalid syntax',
                            ["f'{,}'",
                             "f'{,}'",  # this is (,), which is an error
                             ])

        self.assertAllRaise(SyntaxError, "f-string: expecting '}'",
                            ["f'{3)+(4}'",
                             ])

        self.assertAllRaise(SyntaxError, 'EOL while scanning string literal',
                            ["f'{\n}'",
                             ])

    def test_backslashes_in_string_part(self):
        self.assertEqual(f'\t', '\t')
        self.assertEqual(r'\t', '\\t')
        self.assertEqual(rf'\t', '\\t')
        self.assertEqual(f'{2}\t', '2\t')
        self.assertEqual(f'{2}\t{3}', '2\t3')
        self.assertEqual(f'\t{3}', '\t3')

        self.assertEqual(f'\u0394', '\u0394')
        self.assertEqual(r'\u0394', '\\u0394')
        self.assertEqual(rf'\u0394', '\\u0394')
        self.assertEqual(f'{2}\u0394', '2\u0394')
        self.assertEqual(f'{2}\u0394{3}', '2\u03943')
        self.assertEqual(f'\u0394{3}', '\u03943')

        self.assertEqual(f'\U00000394', '\u0394')
        self.assertEqual(r'\U00000394', '\\U00000394')
        self.assertEqual(rf'\U00000394', '\\U00000394')
        self.assertEqual(f'{2}\U00000394', '2\u0394')
        self.assertEqual(f'{2}\U00000394{3}', '2\u03943')
        self.assertEqual(f'\U00000394{3}', '\u03943')

        self.assertEqual(f'\N{GREEK CAPITAL LETTER DELTA}', '\u0394')
        self.assertEqual(f'{2}\N{GREEK CAPITAL LETTER DELTA}', '2\u0394')
        self.assertEqual(f'{2}\N{GREEK CAPITAL LETTER DELTA}{3}', '2\u03943')
        self.assertEqual(f'\N{GREEK CAPITAL LETTER DELTA}{3}', '\u03943')
        self.assertEqual(f'2\N{GREEK CAPITAL LETTER DELTA}', '2\u0394')
        self.assertEqual(f'2\N{GREEK CAPITAL LETTER DELTA}3', '2\u03943')
        self.assertEqual(f'\N{GREEK CAPITAL LETTER DELTA}3', '\u03943')

        self.assertEqual(f'\x20', ' ')
        self.assertEqual(r'\x20', '\\x20')
        self.assertEqual(rf'\x20', '\\x20')
        self.assertEqual(f'{2}\x20', '2 ')
        self.assertEqual(f'{2}\x20{3}', '2 3')
        self.assertEqual(f'\x20{3}', ' 3')

        self.assertEqual(f'2\x20', '2 ')
        self.assertEqual(f'2\x203', '2 3')
        self.assertEqual(f'\x203', ' 3')

    def test_misformed_unicode_character_name(self):
        # These test are needed because unicode names are parsed
        # differently inside f-strings.
        self.assertAllRaise(SyntaxError, r"\(unicode error\) 'unicodeescape' codec can't decode bytes in position .*: malformed \\N character escape",
                            [r"f'\N'",
                             r"f'\N{'",
                             r"f'\N{GREEK CAPITAL LETTER DELTA'",

                             # Here are the non-f-string versions,
                             #  which should give the same errors.
                             r"'\N'",
                             r"'\N{'",
                             r"'\N{GREEK CAPITAL LETTER DELTA'",
                             ])

    def test_no_backslashes_in_expression_part(self):
        self.assertAllRaise(SyntaxError, 'f-string expression part cannot include a backslash',
                            [r"f'{\'a\'}'",
                             r"f'{\t3}'",
                             r"f'{\}'",
                             r"rf'{\'a\'}'",
                             r"rf'{\t3}'",
                             r"rf'{\}'",
                             r"""rf'{"\N{LEFT CURLY BRACKET}"}'""",
                             ])

    def test_no_escapes_for_braces(self):
        # \x7b is '{'.  Make sure it doesn't start an expression.
        self.assertEqual(f'\x7b2}}', '{2}')
        self.assertEqual(f'\x7b2', '{2')
        self.assertEqual(f'\u007b2', '{2')
        self.assertEqual(f'\N{LEFT CURLY BRACKET}2\N{RIGHT CURLY BRACKET}', '{2}')

    def test_newlines_in_expressions(self):
        self.assertEqual(f'{0}', '0')
        self.assertEqual(rf'''{3+
4}''', '7')

    def test_lambda(self):
        x = 5
        self.assertEqual(f'{(lambda y:x*y)("8")!r}', "'88888'")
        self.assertEqual(f'{(lambda y:x*y)("8")!r:10}', "'88888'   ")
        self.assertEqual(f'{(lambda y:x*y)("8"):10}', "88888     ")

        # lambda doesn't work without parens, because the colon
        #  makes the parser think it's a format_spec
        self.assertAllRaise(SyntaxError, 'unexpected EOF while parsing',
                            ["f'{lambda x:x}'",
                             ])

    def test_yield(self):
        # Not terribly useful, but make sure the yield turns
        #  a function into a generator
        def fn(y):
            f'y:{yield y*2}'

        g = fn(4)
        self.assertEqual(next(g), 8)

    def test_yield_send(self):
        def fn(x):
            yield f'x:{yield (lambda i: x * i)}'

        g = fn(10)
        the_lambda = next(g)
        self.assertEqual(the_lambda(4), 40)
        self.assertEqual(g.send('string'), 'x:string')

    def test_expressions_with_triple_quoted_strings(self):
        self.assertEqual(f"{'''x'''}", 'x')
        self.assertEqual(f"{'''eric's'''}", "eric's")

        # Test concatenation within an expression
        self.assertEqual(f'{"x" """eric"s""" "y"}', 'xeric"sy')
        self.assertEqual(f'{"x" """eric"s"""}', 'xeric"s')
        self.assertEqual(f'{"""eric"s""" "y"}', 'eric"sy')
        self.assertEqual(f'{"""x""" """eric"s""" "y"}', 'xeric"sy')
        self.assertEqual(f'{"""x""" """eric"s""" """y"""}', 'xeric"sy')
        self.assertEqual(f'{r"""x""" """eric"s""" """y"""}', 'xeric"sy')

    def test_multiple_vars(self):
        x = 98
        y = 'abc'
        self.assertEqual(f'{x}{y}', '98abc')

        self.assertEqual(f'X{x}{y}', 'X98abc')
        self.assertEqual(f'{x}X{y}', '98Xabc')
        self.assertEqual(f'{x}{y}X', '98abcX')

        self.assertEqual(f'X{x}Y{y}', 'X98Yabc')
        self.assertEqual(f'X{x}{y}Y', 'X98abcY')
        self.assertEqual(f'{x}X{y}Y', '98XabcY')

        self.assertEqual(f'X{x}Y{y}Z', 'X98YabcZ')

    def test_closure(self):
        def outer(x):
            def inner():
                return f'x:{x}'
            return inner

        self.assertEqual(outer('987')(), 'x:987')
        self.assertEqual(outer(7)(), 'x:7')

    def test_arguments(self):
        y = 2
        def f(x, width):
            return f'x={x*y:{width}}'

        self.assertEqual(f('foo', 10), 'x=foofoo    ')
        x = 'bar'
        self.assertEqual(f(10, 10), 'x=        20')

    def test_locals(self):
        value = 123
        self.assertEqual(f'v:{value}', 'v:123')

    def test_missing_variable(self):
        with self.assertRaises(NameError):
            f'v:{value}'

    def test_missing_format_spec(self):
        class O:
            def __format__(self, spec):
                if not spec:
                    return '*'
                return spec

        self.assertEqual(f'{O():x}', 'x')
        self.assertEqual(f'{O()}', '*')
        self.assertEqual(f'{O():}', '*')

        self.assertEqual(f'{3:}', '3')
        self.assertEqual(f'{3!s:}', '3')

    def test_global(self):
        self.assertEqual(f'g:{a_global}', 'g:global variable')
        self.assertEqual(f'g:{a_global!r}', "g:'global variable'")

        a_local = 'local variable'
        self.assertEqual(f'g:{a_global} l:{a_local}',
                         'g:global variable l:local variable')
        self.assertEqual(f'g:{a_global!r}',
                         "g:'global variable'")
        self.assertEqual(f'g:{a_global} l:{a_local!r}',
                         "g:global variable l:'local variable'")

        self.assertIn("module 'unittest' from", f'{unittest}')

    def test_shadowed_global(self):
        a_global = 'really a local'
        self.assertEqual(f'g:{a_global}', 'g:really a local')
        self.assertEqual(f'g:{a_global!r}', "g:'really a local'")

        a_local = 'local variable'
        self.assertEqual(f'g:{a_global} l:{a_local}',
                         'g:really a local l:local variable')
        self.assertEqual(f'g:{a_global!r}',
                         "g:'really a local'")
        self.assertEqual(f'g:{a_global} l:{a_local!r}',
                         "g:really a local l:'local variable'")

    def test_call(self):
        def foo(x):
            return 'x=' + str(x)

        self.assertEqual(f'{foo(10)}', 'x=10')

    def test_nested_fstrings(self):
        y = 5
        self.assertEqual(f'{f"{0}"*3}', '000')
        self.assertEqual(f'{f"{y}"*3}', '555')

    def test_invalid_string_prefixes(self):
        self.assertAllRaise(SyntaxError, 'unexpected EOF while parsing',
                            ["fu''",
                             "uf''",
                             "Fu''",
                             "fU''",
                             "Uf''",
                             "uF''",
                             "ufr''",
                             "urf''",
                             "fur''",
                             "fru''",
                             "rfu''",
                             "ruf''",
                             "FUR''",
                             "Fur''",
                             "fb''",
                             "fB''",
                             "Fb''",
                             "FB''",
                             "bf''",
                             "bF''",
                             "Bf''",
                             "BF''",
                             ])

    def test_leading_trailing_spaces(self):
        self.assertEqual(f'{ 3}', '3')
        self.assertEqual(f'{  3}', '3')
        self.assertEqual(f'{3 }', '3')
        self.assertEqual(f'{3  }', '3')

        self.assertEqual(f'expr={ {x: y for x, y in [(1, 2), ]}}',
                         'expr={1: 2}')
        self.assertEqual(f'expr={ {x: y for x, y in [(1, 2), ]} }',
                         'expr={1: 2}')

    def test_not_equal(self):
        # There's a special test for this because there's a special
        #  case in the f-string parser to look for != as not ending an
        #  expression. Normally it would, while looking for !s or !r.

        self.assertEqual(f'{3!=4}', 'True')
        self.assertEqual(f'{3!=4:}', 'True')
        self.assertEqual(f'{3!=4!s}', 'True')
        self.assertEqual(f'{3!=4!s:.3}', 'Tru')

    def test_conversions(self):
        self.assertEqual(f'{3.14:10.10}', '      3.14')
        self.assertEqual(f'{3.14!s:10.10}', '3.14      ')
        self.assertEqual(f'{3.14!r:10.10}', '3.14      ')
        self.assertEqual(f'{3.14!a:10.10}', '3.14      ')

        self.assertEqual(f'{"a"}', 'a')
        self.assertEqual(f'{"a"!r}', "'a'")
        self.assertEqual(f'{"a"!a}', "'a'")

        # Not a conversion.
        self.assertEqual(f'{"a!r"}', "a!r")

        # Not a conversion, but show that ! is allowed in a format spec.
        self.assertEqual(f'{3.14:!<10.10}', '3.14!!!!!!')

        self.assertAllRaise(SyntaxError, 'f-string: invalid conversion character',
                            ["f'{3!g}'",
                             "f'{3!A}'",
                             "f'{3!3}'",
                             "f'{3!G}'",
                             "f'{3!!}'",
                             "f'{3!:}'",
                             "f'{3! s}'",  # no space before conversion char
                             ])

        self.assertAllRaise(SyntaxError, "f-string: expecting '}'",
                            ["f'{x!s{y}}'",
                             "f'{3!ss}'",
                             "f'{3!ss:}'",
                             "f'{3!ss:s}'",
                             ])

    def test_assignment(self):
        self.assertAllRaise(SyntaxError, 'invalid syntax',
                            ["f'' = 3",
                             "f'{0}' = x",
                             "f'{x}' = x",
                             ])

    def test_del(self):
        self.assertAllRaise(SyntaxError, 'invalid syntax',
                            ["del f''",
                             "del '' f''",
                             ])

    def test_mismatched_braces(self):
        self.assertAllRaise(SyntaxError, "f-string: single '}' is not allowed",
                            ["f'{{}'",
                             "f'{{}}}'",
                             "f'}'",
                             "f'x}'",
                             "f'x}x'",

                             # Can't have { or } in a format spec.
                             "f'{3:}>10}'",
                             "f'{3:}}>10}'",
                             ])

        self.assertAllRaise(SyntaxError, "f-string: expecting '}'",
                            ["f'{3:{{>10}'",
                             "f'{3'",
                             "f'{3!'",
                             "f'{3:'",
                             "f'{3!s'",
                             "f'{3!s:'",
                             "f'{3!s:3'",
                             "f'x{'",
                             "f'x{x'",
                             "f'{x'",
                             "f'{3:s'",
                             "f'{{{'",
                             "f'{{}}{'",
                             "f'{'",
                             ])

        # But these are just normal strings.
        self.assertEqual(f'{"{"}', '{')
        self.assertEqual(f'{"}"}', '}')
        self.assertEqual(f'{3:{"}"}>10}', '}}}}}}}}}3')
        self.assertEqual(f'{2:{"{"}>10}', '{{{{{{{{{2')

    def test_if_conditional(self):
        # There's special logic in compile.c to test if the
        #  conditional for an if (and while) are constants. Exercise
        #  that code.

        def test_fstring(x, expected):
            flag = 0
            if f'{x}':
                flag = 1
            else:
                flag = 2
            self.assertEqual(flag, expected)

        def test_concat_empty(x, expected):
            flag = 0
            if '' f'{x}':
                flag = 1
            else:
                flag = 2
            self.assertEqual(flag, expected)

        def test_concat_non_empty(x, expected):
            flag = 0
            if ' ' f'{x}':
                flag = 1
            else:
                flag = 2
            self.assertEqual(flag, expected)

        test_fstring('', 2)
        test_fstring(' ', 1)

        test_concat_empty('', 2)
        test_concat_empty(' ', 1)

        test_concat_non_empty('', 1)
        test_concat_non_empty(' ', 1)

    def test_empty_format_specifier(self):
        x = 'test'
        self.assertEqual(f'{x}', 'test')
        self.assertEqual(f'{x:}', 'test')
        self.assertEqual(f'{x!s:}', 'test')
        self.assertEqual(f'{x!r:}', "'test'")

    def test_str_format_differences(self):
        d = {'a': 'string',
             0: 'integer',
             }
        a = 0
        self.assertEqual(f'{d[0]}', 'integer')
        self.assertEqual(f'{d["a"]}', 'string')
        self.assertEqual(f'{d[a]}', 'integer')
        self.assertEqual('{d[a]}'.format(d=d), 'string')
        self.assertEqual('{d[0]}'.format(d=d), 'integer')

    def test_invalid_expressions(self):
        self.assertAllRaise(SyntaxError, 'invalid syntax',
                            [r"f'{a[4)}'",
                             r"f'{a(4]}'",
                            ])

    def test_errors(self):
        # see issue 26287
        self.assertAllRaise(TypeError, 'non-empty',
                            [r"f'{(lambda: 0):x}'",
                             r"f'{(0,):x}'",
                             ])
        self.assertAllRaise(ValueError, 'Unknown format code',
                            [r"f'{1000:j}'",
                             r"f'{1000:j}'",
                            ])

    def test_loop(self):
        for i in range(1000):
            self.assertEqual(f'i:{i}', 'i:' + str(i))

    def test_dict(self):
        d = {'"': 'dquote',
             "'": 'squote',
             'foo': 'bar',
             }
        self.assertEqual(f'''{d["'"]}''', 'squote')
        self.assertEqual(f"""{d['"']}""", 'dquote')

        self.assertEqual(f'{d["foo"]}', 'bar')
        self.assertEqual(f"{d['foo']}", 'bar')

if __name__ == '__main__':
    unittest.main()