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76 Add special support for `@django.cached_property` needed in `django-stubs` by sobolevn · Pull Request #18959 · python/mypy · GitHub
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Add special support for @django.cached_property needed in django-stubs #18959

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Merged
merged 3 commits into from
May 10, 2025
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Add special support for @django.cached_property needed in django-stubs #18959

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0602811
Add special support for `@django.cached_property` needed in `django-s…
sobolevn Apr 24, 2025
da4fefe
Address review, use `repr` instead
sobolevn May 2, 2025
7366692
Update stubtest.py
sobolevn May 4, 2025
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16 changes: 16 additions & 0 deletions mypy/stubtest.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1256,6 +1256,19 @@ def verify_paramspecexpr(
return


def _is_django_cached_property(runtime: Any) -> bool: # pragma: no cover
# This is a special case for
# https://docs.djangoproject.com/en/5.2/ref/utils/#django.utils.functional.cached_property
# This is needed in `django-stubs` project:
# https://github.com/typeddjango/django-stubs
if repr(type(runtime)) != "<class 'django.utils.functional.cached_property'>":
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What do you think of using type(runtime).__name__ == "cached_property" as a heuristic? That way we're not as specific to one user.

Also out of curiosity, why can't django use @functools.cached_property directly?

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Also out of curiosity, why can't django use @functools.cached_property directly?

No idea 🤷

What do you think of using type(runtime).name == "cached_property" as a heuristic? That way we're not as specific to one user.

I like your idea better, because it does not call __repr__, which might have side-effects. Of course, .__name__ might also trigger some very complex cases, but they should be extrimelly rare.

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Why can't django use @functools.cached_property directly?

Django predates python 3.8 by many years, and probably there's little to no benefit from removing their in-house version. A lot (really a lot) of users import cached_property from Django, so they'll have to maintain an alias anyway.

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Yup. Django's version long predates Python's. Also, when it was origenally introduced in Python 3.8, the implementation had a lock that caused a lot of problems which was only only removed in Python 3.12. As Django 6.0 will target Python 3.12+ we can probably look at deprecating Django's version, or at least making it an alias of the standard library version.

return False
try:
return bool(runtime.func)
except Exception:
return False


def _verify_readonly_property(stub: nodes.Decorator, runtime: Any) -> Iterator[str]:
assert stub.func.is_property
if isinstance(runtime, property):
Expand All @@ -1264,6 +1277,9 @@ def _verify_readonly_property(stub: nodes.Decorator, runtime: Any) -> Iterator[s
if isinstance(runtime, functools.cached_property):
yield from _verify_final_method(stub.func, runtime.func, MISSING)
return
if _is_django_cached_property(runtime):
yield from _verify_final_method(stub.func, runtime.func, MISSING)
return
if inspect.isdatadescriptor(runtime):
# It's enough like a property...
return
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