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bpo-44799: Fix InitVar resolving using get_type_hints by uriyyo · Pull Request #27553 · python/cpython · GitHub

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bpo-44799: Fix InitVar resolving using get_type_hints #27553

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bpo-44799: Fix InitVar resolving using get_type_hints #27553

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3 changes: 3 additions & 0 deletions Lib/dataclasses.py
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Expand Up @@ -228,6 +228,9 @@ class InitVar:
def __init__(self, type):
self.type = type

def __call__(self, *args, **kwargs): # required by typing.get_type_hints, see bpo-44799

ericvsmith Aug 2, 2021

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

How does this solve the problem at hand?

I'm unlikely to accept any changes to dataclasses and typing until PEP 649 is ruled on.

uriyyo Aug 2, 2021

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Exception raised by _type_check. In case if object is callable this object won't raise exception.

cpython/Lib/typing.py

Lines 180 to 181 in e06ae75

if not callable(arg):
raise TypeError(f"{msg} Got {arg!r:.100}.")

I found that it was the easiest way to solve this issue. If you think it's a bad solution I am open to fix it in another way.

ericvsmith Aug 2, 2021

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

It just seems like it's papering over some actual problem.

In any event, I'm waiting on PEP 649, which if accepted makes this whole point moot.

uriyyo Aug 2, 2021

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Makes sense, will wait on a update regarding PEP 649.
raise TypeError("InitVar object is not callable")

def __repr__(self):
if isinstance(self.type, type):
type_name = self.type.__name__
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14 changes: 14 additions & 0 deletions Lib/test/test_dataclasses.py
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Expand Up @@ -3831,5 +3831,19 @@ class A:
c: int = 1
d: int

def test_lazy_init_var_get_type_hints(self):
@dataclass
class Foo:
a: "InitVar[int]"

hints = get_type_hints(Foo)

self.assertIsInstance(hints.get("a"), InitVar)
self.assertEqual(hints.get("a").type, int)

def test_init_var_is_not_callable(self):
with self.assertRaisesRegex(TypeError, r"InitVar object is not callable"):
InitVar[int]()

if __name__ == '__main__':
unittest.main()
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2021-08-02-16-21-59.bpo-44799.hXfxPO.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix issue when ``dataclass.InitVar`` can not be evaluated using
``typing.get_type_hints``. Patch provided by Yurii Karabas.
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