[issue45359] TopologicalSorter is not Generic at runtime (but is in typeshed)

[Jacob Hayes]

Jacob Hayes  added the comment:

Thanks for the tips! I've been using this patch in my own code in a early 
imported `__init__.py`:

```
from graphlib import TopologicalSorter
from types import GenericAlias

if not hasattr(TopologicalSorter, "__class_getitem__"):  # pragma: no cover
TopologicalSorter.__class_getitem__ = classmethod(GenericAlias)  # type: 
ignore
```

Certainly a bit hacky, but aside from no-op on >=3.11 and satisfying mypy, it 
supports runtime type inspection via `get_type_hints` before 3.11 (which 
otherwise still errors for stringized versions). The stringized versions are 
probably a bit simpler/safer for most folks though :)

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[issue45167] deepcopy of GenericAlias with __deepcopy__ method is broken

[Jacob Hayes]

New submission from Jacob Hayes :

When deepcopying a parametrized types.GenericAlias (eg: a dict subclass) that 
has a __deepcopy__ method, the copy module doesn't detect the GenericAlias as a 
type and instead tries to call cls.__deepcopy__, passing `memo` inplace of 
self. This doesn't seem to happen with `typing.Generic` however.

Example:
```
from copy import deepcopy


class X(dict):
def __deepcopy__(self, memo):
return self


print(deepcopy(X()))
print(deepcopy(X))

print(type(X[str, int]))
print(deepcopy(X[str, int]()))
print(deepcopy(X[str, int]))
```
shows
```
{}


{}
Traceback (most recent call last):
  File "/tmp/demo.py", line 14, in 
print(deepcopy(X[str, int]))
  File "/Users/jacobhayes/.pyenv/versions/3.9.6/lib/python3.9/copy.py", line 
153, in deepcopy
y = copier(memo)
TypeError: __deepcopy__() missing 1 required positional argument: 'memo'
```

I don't know if it's better to update `copy.deepcopy` here or perhaps narrow 
the `__getattr__` for `types.GenericAlias` (as `typing. _BaseGenericAlias` 
seems to).

--
components: Library (Lib)
messages: 401601
nosy: JacobHayes
priority: normal
severity: normal
status: open
title: deepcopy of GenericAlias with __deepcopy__ method is broken
type: behavior
versions: Python 3.9

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[issue45359] TopologicalSorter is not Generic at runtime (but is in typeshed)

[Jacob Hayes]

New submission from Jacob Hayes :

Reproduction:

```
from graphlib import TopologicalSorter

TopologicalSorter[str]({"a": {}, "b": {"a"}})
```
```
$ mypy /tmp/toposort.py
Success: no issues found in 1 source file
$ python3 /tmp/toposort.py
Traceback (most recent call last):
  File "/tmp/toposort.py", line 3, in 
TopologicalSorter[str]({"a": {}, "b": {"a"}})
TypeError: 'type' object is not subscriptable
```

I opened the issue here (rather than typeshed) because we'd presumably like to 
support this at runtime too.

Typeshed link: 
https://github.com/python/mypy/blob/0a830481980bfc554ded61a3eaaaecde384a21e4/mypy/typeshed/stdlib/graphlib.pyi#L6

--
components: Library (Lib)
messages: 403115
nosy: JacobHayes
priority: normal
severity: normal
status: open
title: TopologicalSorter is not Generic at runtime (but is in typeshed)
type: behavior
versions: Python 3.9

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[issue45359] TopologicalSorter is not Generic at runtime (but is in typeshed)

[Jacob Hayes]

Change by Jacob Hayes :


--
keywords: +patch
pull_requests: +27064
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/28714

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[issue45359] TopologicalSorter is not Generic at runtime (but is in typeshed)

[Jacob Hayes]

Jacob Hayes  added the comment:

Thanks for merging!

Should typeshed be updated for <3.11 in the meantime or do you suggest `if 
TYPE_CHECKING` blocks on user side? Perhaps it's a non-issue if no one else has 
noticed this. :)

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