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bpo-41370: Evaluate strings as forward refs in PEP 585 generics #30900

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Merged
merged 10 commits into from
Mar 7, 2022
Merged

bpo-41370: Evaluate strings as forward refs in PEP 585 generics #30900

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e820e3a
convert strings in PEP 585 generic aliases (`types.GenericAlias`) to …
NiklasRosenstein Jan 25, 2022
d7f57c7
add unittest for new get_type_hints() behaviour on PEP 585 generics w…
NiklasRosenstein Jan 25, 2022
26ab740
add unit test for `from __future__ import annotations`
NiklasRosenstein Jan 27, 2022
a04bd5d
add test for recursive type
NiklasRosenstein Jan 27, 2022
3416713
📜🤖 Added by blurb_it.
blurb-it[bot] Jan 27, 2022
30a3564
Double backticks because RST.
NiklasRosenstein Jan 27, 2022
13a3505
Update Lib/typing.py
NiklasRosenstein Jan 27, 2022
33d286a
Update Misc/NEWS.d/next/Library/2022-01-27-11-54-16.bpo-41370.gYxCPE.rst
NiklasRosenstein Jan 27, 2022
6cd96b1
Merge branch 'main' into issue41370
NiklasRosenstein Feb 22, 2022
39c5b06
Replace assertIs with assertEqual in test_get_type_hints_annotated
NiklasRosenstein Mar 3, 2022
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44 changes: 42 additions & 2 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@
from typing import ParamSpec, Concatenate, ParamSpecArgs, ParamSpecKwargs
from typing import TypeGuard
import abc
import textwrap
import typing
import weakref
import types
Expand Down Expand Up @@ -2006,6 +2007,45 @@ def barfoo(x: AT): ...
def barfoo2(x: CT): ...
self.assertIs(get_type_hints(barfoo2, globals(), locals())['x'], CT)

def test_generic_pep585_forward_ref(self):
# See https://bugs.python.org/issue41370

class C1:
a: list['C1']
self.assertEqual(
get_type_hints(C1, globals(), locals()),
{'a': list[C1]}
)

class C2:
a: dict['C1', list[List[list['C2']]]]
self.assertEqual(
get_type_hints(C2, globals(), locals()),
{'a': dict[C1, list[List[list[C2]]]]}
)

# Test stringified annotations
scope = {}
exec(textwrap.dedent('''
from __future__ import annotations
class C3:
a: List[list["C2"]]
'''), scope)
C3 = scope['C3']
self.assertEqual(C3.__annotations__['a'], "List[list['C2']]")
self.assertEqual(
get_type_hints(C3, globals(), locals()),
{'a': List[list[C2]]}
)

# Test recursive types
X = list["X"]
def f(x: X): ...
self.assertEqual(
get_type_hints(f, globals(), locals()),
{'x': list[list[ForwardRef('X')]]}
)

def test_extended_generic_rules_subclassing(self):
class T1(Tuple[T, KT]): ...
class T2(Tuple[T, ...]): ...
Expand Down Expand Up @@ -3270,15 +3310,15 @@ def foobar(x: list[ForwardRef('X')]): ...
BA = Tuple[Annotated[T, (1, 0)], ...]
def barfoo(x: BA): ...
self.assertEqual(get_type_hints(barfoo, globals(), locals())['x'], Tuple[T, ...])
self.assertIs(
self.assertEqual(
get_type_hints(barfoo, globals(), locals(), include_extras=True)['x'],
BA
)

BA = tuple[Annotated[T, (1, 0)], ...]
def barfoo(x: BA): ...
self.assertEqual(get_type_hints(barfoo, globals(), locals())['x'], tuple[T, ...])
self.assertIs(
self.assertEqual(
get_type_hints(barfoo, globals(), locals(), include_extras=True)['x'],
BA
)
Expand Down
6 changes: 6 additions & 0 deletions Lib/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -331,6 +331,12 @@ def _eval_type(t, globalns, localns, recursive_guard=frozenset()):
if isinstance(t, ForwardRef):
return t._evaluate(globalns, localns, recursive_guard)
if isinstance(t, (_GenericAlias, GenericAlias, types.UnionType)):
if isinstance(t, GenericAlias):
args = tuple(
ForwardRef(arg) if isinstance(arg, str) else arg
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Do we need to pass globals and locals to ForwardRef here? 🤔

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I may not be knowledgable enough about the typing code base, but I don't see a globals/locals argument for ForwardRef. Do you mean the module? I couldn't find out how to use/what to pass to that argument exactly.

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It's too late for that anyway. The ForwardRef class has an optional module= argument which may be used to resolve references, but the best we could do at this point is passing globalns.get("__name__"), which would just end up with the same globalns as we are using anyway.

This suggests there could still be scenarios where this will fail, esp. when a type alias defined in one module is used in another. But that would only be solvable by recording the module at the time the alias is being defined, and we've already said we wouldn't go that far (since it would require a ForwardRef implementation in C).

for arg in t.__args__
)
t = t.__origin__[args]
ev_args = tuple(_eval_type(a, globalns, localns, recursive_guard) for a in t.__args__)
if ev_args == t.__args__:
return t
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2022-01-27-11-54-16.bpo-41370.gYxCPE.rst
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@@ -0,0 +1 @@
:func:`typing.get_type_hints` now supports evaluating strings as forward references in :ref:`PEP 585 generic aliases <types-genericalias>`.