bpo-38605: Make 'from __future__ import annotations' the default (GH-20434)
The hard part was making all the tests pass; there are some subtle issues here, because apparently the future import wasn't tested very thoroughly in previous Python versions.
For example, `inspect.signature()` returned type objects normally (except for forward references), but strings with the future import. We changed it to try and return type objects by calling `typing.get_type_hints()`, but fall back on returning strings if that function fails (which it may do if there are future references in the annotations that require passing in a specific namespace to resolve).
diff --git a/Lib/test/test_annotations.py b/Lib/test/test_annotations.py
new file mode 100644
index 0000000..3e6b709
--- /dev/null
+++ b/Lib/test/test_annotations.py
@@ -0,0 +1,228 @@
+import unittest
+import sys
+from textwrap import dedent
+
+class PostponedAnnotationsTestCase(unittest.TestCase):
+ template = dedent(
+ """
+ def f() -> {ann}:
+ ...
+ def g(arg: {ann}) -> None:
+ ...
+ async def f2() -> {ann}:
+ ...
+ async def g2(arg: {ann}) -> None:
+ ...
+ var: {ann}
+ var2: {ann} = None
+ """
+ )
+
+ def getActual(self, annotation):
+ scope = {}
+ exec(self.template.format(ann=annotation), {}, scope)
+ func_ret_ann = scope['f'].__annotations__['return']
+ func_arg_ann = scope['g'].__annotations__['arg']
+ async_func_ret_ann = scope['f2'].__annotations__['return']
+ async_func_arg_ann = scope['g2'].__annotations__['arg']
+ var_ann1 = scope['__annotations__']['var']
+ var_ann2 = scope['__annotations__']['var2']
+ self.assertEqual(func_ret_ann, func_arg_ann)
+ self.assertEqual(func_ret_ann, async_func_ret_ann)
+ self.assertEqual(func_ret_ann, async_func_arg_ann)
+ self.assertEqual(func_ret_ann, var_ann1)
+ self.assertEqual(func_ret_ann, var_ann2)
+ return func_ret_ann
+
+ def assertAnnotationEqual(
+ self, annotation, expected=None, drop_parens=False, is_tuple=False,
+ ):
+ actual = self.getActual(annotation)
+ if expected is None:
+ expected = annotation if not is_tuple else annotation[1:-1]
+ if drop_parens:
+ self.assertNotEqual(actual, expected)
+ actual = actual.replace("(", "").replace(")", "")
+
+ self.assertEqual(actual, expected)
+
+ def test_annotations(self):
+ eq = self.assertAnnotationEqual
+ eq('...')
+ eq("'some_string'")
+ eq("u'some_string'")
+ eq("b'\\xa3'")
+ eq('Name')
+ eq('None')
+ eq('True')
+ eq('False')
+ eq('1')
+ eq('1.0')
+ eq('1j')
+ eq('True or False')
+ eq('True or False or None')
+ eq('True and False')
+ eq('True and False and None')
+ eq('Name1 and Name2 or Name3')
+ eq('Name1 and (Name2 or Name3)')
+ eq('Name1 or Name2 and Name3')
+ eq('(Name1 or Name2) and Name3')
+ eq('Name1 and Name2 or Name3 and Name4')
+ eq('Name1 or Name2 and Name3 or Name4')
+ eq('a + b + (c + d)')
+ eq('a * b * (c * d)')
+ eq('(a ** b) ** c ** d')
+ eq('v1 << 2')
+ eq('1 >> v2')
+ eq('1 % finished')
+ eq('1 + v2 - v3 * 4 ^ 5 ** v6 / 7 // 8')
+ eq('not great')
+ eq('not not great')
+ eq('~great')
+ eq('+value')
+ eq('++value')
+ eq('-1')
+ eq('~int and not v1 ^ 123 + v2 | True')
+ eq('a + (not b)')
+ eq('lambda: None')
+ eq('lambda arg: None')
+ eq('lambda a=True: a')
+ eq('lambda a, b, c=True: a')
+ eq("lambda a, b, c=True, *, d=1 << v2, e='str': a")
+ eq("lambda a, b, c=True, *vararg, d, e='str', **kwargs: a + b")
+ eq("lambda a, /, b, c=True, *vararg, d, e='str', **kwargs: a + b")
+ eq('lambda x, /: x')
+ eq('lambda x=1, /: x')
+ eq('lambda x, /, y: x + y')
+ eq('lambda x=1, /, y=2: x + y')
+ eq('lambda x, /, y=1: x + y')
+ eq('lambda x, /, y=1, *, z=3: x + y + z')
+ eq('lambda x=1, /, y=2, *, z=3: x + y + z')
+ eq('lambda x=1, /, y=2, *, z: x + y + z')
+ eq('lambda x=1, y=2, z=3, /, w=4, *, l, l2: x + y + z + w + l + l2')
+ eq('lambda x=1, y=2, z=3, /, w=4, *, l, l2, **kwargs: x + y + z + w + l + l2')
+ eq('lambda x, /, y=1, *, z: x + y + z')
+ eq('lambda x: lambda y: x + y')
+ eq('1 if True else 2')
+ eq('str or None if int or True else str or bytes or None')
+ eq('str or None if (1 if True else 2) else str or bytes or None')
+ eq("0 if not x else 1 if x > 0 else -1")
+ eq("(1 if x > 0 else -1) if x else 0")
+ eq("{'2.7': dead, '3.7': long_live or die_hard}")
+ eq("{'2.7': dead, '3.7': long_live or die_hard, **{'3.6': verygood}}")
+ eq("{**a, **b, **c}")
+ eq("{'2.7', '3.6', '3.7', '3.8', '3.9', '4.0' if gilectomy else '3.10'}")
+ eq("{*a, *b, *c}")
+ eq("({'a': 'b'}, True or False, +value, 'string', b'bytes') or None")
+ eq("()")
+ eq("(a,)")
+ eq("(a, b)")
+ eq("(a, b, c)")
+ eq("(*a, *b, *c)")
+ eq("[]")
+ eq("[1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or A, 11 or B, 12 or C]")
+ eq("[*a, *b, *c]")
+ eq("{i for i in (1, 2, 3)}")
+ eq("{i ** 2 for i in (1, 2, 3)}")
+ eq("{i ** 2 for i, _ in ((1, 'a'), (2, 'b'), (3, 'c'))}")
+ eq("{i ** 2 + j for i in (1, 2, 3) for j in (1, 2, 3)}")
+ eq("[i for i in (1, 2, 3)]")
+ eq("[i ** 2 for i in (1, 2, 3)]")
+ eq("[i ** 2 for i, _ in ((1, 'a'), (2, 'b'), (3, 'c'))]")
+ eq("[i ** 2 + j for i in (1, 2, 3) for j in (1, 2, 3)]")
+ eq("(i for i in (1, 2, 3))")
+ eq("(i ** 2 for i in (1, 2, 3))")
+ eq("(i ** 2 for i, _ in ((1, 'a'), (2, 'b'), (3, 'c')))")
+ eq("(i ** 2 + j for i in (1, 2, 3) for j in (1, 2, 3))")
+ eq("{i: 0 for i in (1, 2, 3)}")
+ eq("{i: j for i, j in ((1, 'a'), (2, 'b'), (3, 'c'))}")
+ eq("[(x, y) for x, y in (a, b)]")
+ eq("[(x,) for x, in (a,)]")
+ eq("Python3 > Python2 > COBOL")
+ eq("Life is Life")
+ eq("call()")
+ eq("call(arg)")
+ eq("call(kwarg='hey')")
+ eq("call(arg, kwarg='hey')")
+ eq("call(arg, *args, another, kwarg='hey')")
+ eq("call(arg, another, kwarg='hey', **kwargs, kwarg2='ho')")
+ eq("lukasz.langa.pl")
+ eq("call.me(maybe)")
+ eq("1 .real")
+ eq("1.0.real")
+ eq("....__class__")
+ eq("list[str]")
+ eq("dict[str, int]")
+ eq("set[str,]")
+ eq("tuple[str, ...]")
+ eq("tuple[(str, *types)]")
+ eq("tuple[str, int, (str, int)]")
+ eq("tuple[(*int, str, str, (str, int))]")
+ eq("tuple[str, int, float, dict[str, int]]")
+ eq("slice[0]")
+ eq("slice[0:1]")
+ eq("slice[0:1:2]")
+ eq("slice[:]")
+ eq("slice[:-1]")
+ eq("slice[1:]")
+ eq("slice[::-1]")
+ eq("slice[:,]")
+ eq("slice[1:2,]")
+ eq("slice[1:2:3,]")
+ eq("slice[1:2, 1]")
+ eq("slice[1:2, 2, 3]")
+ eq("slice[()]")
+ eq("slice[a, b:c, d:e:f]")
+ eq("slice[(x for x in a)]")
+ eq('str or None if sys.version_info[0] > (3,) else str or bytes or None')
+ eq("f'f-string without formatted values is just a string'")
+ eq("f'{{NOT a formatted value}}'")
+ eq("f'some f-string with {a} {few():.2f} {formatted.values!r}'")
+ eq('''f"{f'{nested} inner'} outer"''')
+ eq("f'space between opening braces: { {a for a in (1, 2, 3)}}'")
+ eq("f'{(lambda x: x)}'")
+ eq("f'{(None if a else lambda x: x)}'")
+ eq("f'{x}'")
+ eq("f'{x!r}'")
+ eq("f'{x!a}'")
+ eq('(yield from outside_of_generator)')
+ eq('(yield)')
+ eq('(yield a + b)')
+ eq('await some.complicated[0].call(with_args=True or 1 is not 1)')
+ eq('[x for x in (a if b else c)]')
+ eq('[x for x in a if (b if c else d)]')
+ eq('f(x for x in a)')
+ eq('f(1, (x for x in a))')
+ eq('f((x for x in a), 2)')
+ eq('(((a)))', 'a')
+ eq('(((a, b)))', '(a, b)')
+ eq("(x := 10)")
+ eq("f'{(x := 10):=10}'")
+ eq("1 + 2")
+ eq("1 + 2 + 3")
+
+ def test_fstring_debug_annotations(self):
+ # f-strings with '=' don't round trip very well, so set the expected
+ # result explicitely.
+ self.assertAnnotationEqual("f'{x=!r}'", expected="f'x={x!r}'")
+ self.assertAnnotationEqual("f'{x=:}'", expected="f'x={x:}'")
+ self.assertAnnotationEqual("f'{x=:.2f}'", expected="f'x={x:.2f}'")
+ self.assertAnnotationEqual("f'{x=!r}'", expected="f'x={x!r}'")
+ self.assertAnnotationEqual("f'{x=!a}'", expected="f'x={x!a}'")
+ self.assertAnnotationEqual("f'{x=!s:*^20}'", expected="f'x={x!s:*^20}'")
+
+ def test_infinity_numbers(self):
+ inf = "1e" + repr(sys.float_info.max_10_exp + 1)
+ infj = f"{inf}j"
+ self.assertAnnotationEqual("1e1000", expected=inf)
+ self.assertAnnotationEqual("1e1000j", expected=infj)
+ self.assertAnnotationEqual("-1e1000", expected=f"-{inf}")
+ self.assertAnnotationEqual("3+1e1000j", expected=f"3 + {infj}")
+ self.assertAnnotationEqual("(1e1000, 1e1000j)", expected=f"({inf}, {infj})")
+ self.assertAnnotationEqual("'inf'")
+ self.assertAnnotationEqual("('inf', 1e1000, 'infxxx', 1e1000j)", expected=f"('inf', {inf}, 'infxxx', {infj})")
+ self.assertAnnotationEqual("(1e1000, (1e1000j,))", expected=f"({inf}, ({infj},))")
+
+
+if __name__ == "__main__":
+ unittest.main()