[issue45326] Unexpected TypeError with type alias+issubclass+ABC

[Andrei Kulakov]

Change by Andrei Kulakov :


--
nosy: +kj
type:  -> behavior

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[issue45326] Unexpected TypeError with type alias+issubclass+ABC

[Andrei Kulakov]

Andrei Kulakov  added the comment:

This error was added in https://bugs.python.org/issue33018 . See some 
discussion on that issue.

Note that first arg needs to be a type (i.e. instance of `type`) to avoid this 
error:

[ins] In [41]: class C(ABC):0

[ins] In [42]: issubclass(dict, C)
Out[42]: False

[ins] In [43]: issubclass('', C)  # TypeError: issubclass() arg 1 must be a 
class

[ins] In [44]: issubclass(typing.Dict, C)   # same error as above

--
nosy: +andrei.avk

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[issue45326] Unexpected TypeError with type alias+issubclass+ABC

[burrito]

Change by burrito :


--
nosy: +burrito

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[issue45326] Unexpected TypeError with type alias+issubclass+ABC

[Dong-hee Na]

Change by Dong-hee Na :


--
versions: +Python 3.10, Python 3.11

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[issue45326] Unexpected TypeError with type alias+issubclass+ABC

[Dong-hee Na]

Change by Dong-hee Na :


--
nosy: +gvanrossum

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[issue45326] Unexpected TypeError with type alias+issubclass+ABC

[Dong-hee Na]

Change by Dong-hee Na :


--
nosy: +corona10

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[issue45326] Unexpected TypeError with type alias+issubclass+ABC

[Dmitry Marakasov]

New submission from Dmitry Marakasov :

Here's a curious problem. issubclass() check of a type against an ABC-derived 
class raises TypeError claiming that type is not a class, however 
inspect.isclass() says it's a class, and issubclass() check against a simple 
class works fine:

```
from abc import ABC

class C1:
pass

issubclass(dict[str, str], C1)  # False

class C2(ABC):
pass

issubclass(dict[str, str], C2)  # TypeError: issubclass() arg 1 must be a class
```

I've ran into this problem while using `inspect` module to look for subclasses 
of a specific ABC in a module which may also contain type aliases, and after 
converting a type alias from `Dict[str, str]` to modern `dict[str, str]` I've 
got an unexpected crash in this code:

if inspect.isclass(member) and issubclass(member, superclass):

Not sure which is the culprit, ABC or how dict[]-style type aliases are 
implemented.

--
components: Library (Lib)
messages: 402914
nosy: AMDmi3
priority: normal
severity: normal
status: open
title: Unexpected TypeError with type alias+issubclass+ABC
versions: Python 3.9

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