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[3.9] bpo-41341: Recursive evaluation of ForwardRef in get_type_hints (GH-21553) #21629

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Merged
miss-islington merged 1 commit into from
Jul 26, 2020
Merged

[3.9] bpo-41341: Recursive evaluation of ForwardRef in get_type_hints (GH-21553) #21629

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6 changes: 6 additions & 0 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2456,6 +2456,12 @@ def foo(a: tuple[ForwardRef('T')]):
self.assertEqual(get_type_hints(foo, globals(), locals()),
{'a': tuple[T]})

def test_double_forward(self):
def foo(a: 'List[\'int\']'):
pass
self.assertEqual(get_type_hints(foo, globals(), locals()),
{'a': List[int]})

def test_forward_recursion_actually(self):
def namespace1():
a = typing.ForwardRef('A')
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20 changes: 14 additions & 6 deletions Lib/typing.py
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Expand Up @@ -244,14 +244,16 @@ def inner(*args, **kwds):
return inner


def _eval_type(t, globalns, localns):
def _eval_type(t, globalns, localns, recursive_guard=frozenset()):
"""Evaluate all forward reverences in the given type t.
For use of globalns and localns see the docstring for get_type_hints().
recursive_guard is used to prevent prevent infinite recursion
with recursive ForwardRef.
"""
if isinstance(t, ForwardRef):
return t._evaluate(globalns, localns)
return t._evaluate(globalns, localns, recursive_guard)
if isinstance(t, (_GenericAlias, GenericAlias)):
ev_args = tuple(_eval_type(a, globalns, localns) for a in t.__args__)
ev_args = tuple(_eval_type(a, globalns, localns, recursive_guard) for a in t.__args__)
if ev_args == t.__args__:
return t
if isinstance(t, GenericAlias):
Expand Down Expand Up @@ -477,18 +479,24 @@ def __init__(self, arg, is_argument=True):
self.__forward_value__ = None
self.__forward_is_argument__ = is_argument

def _evaluate(self, globalns, localns):
def _evaluate(self, globalns, localns, recursive_guard):
if self.__forward_arg__ in recursive_guard:
return self
if not self.__forward_evaluated__ or localns is not globalns:
if globalns is None and localns is None:
globalns = localns = {}
elif globalns is None:
globalns = localns
elif localns is None:
localns = globalns
self.__forward_value__ = _type_check(
type_ =_type_check(
eval(self.__forward_code__, globalns, localns),
"Forward references must evaluate to types.",
is_argument=self.__forward_is_argument__)
is_argument=self.__forward_is_argument__,
)
self.__forward_value__ = _eval_type(
type_, globalns, localns, recursive_guard | {self.__forward_arg__}
)
self.__forward_evaluated__ = True
return self.__forward_value__

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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2020-07-20-19-13-17.bpo-41341.wqrj8C.rst
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@@ -0,0 +1 @@
Recursive evaluation of `typing.ForwardRef` in `get_type_hints`.