TypeError: issubclass() arg 1 must be a class when upgrading to 2.5

[antazoey]

Hello,

Ever since 2.5 was released, all of our CI/CD fails on Python 3.9 and 3.10 with the following error:

../../virtualenvs/ape_310/lib/python3.10/site-packages/pydantic_settings/sources.py:771: in _field_is_complex
    if self.field_is_complex(field):
../../virtualenvs/ape_310/lib/python3.10/site-packages/pydantic_settings/sources.py:276: in field_is_complex
    return _annotation_is_complex(field.annotation, field.metadata)
../../virtualenvs/ape_310/lib/python3.10/site-packages/pydantic_settings/sources.py:2118: in _annotation_is_complex
    if isinstance(annotation, type) and issubclass(annotation, RootModel):
../../.pyenv/versions/3.10.0/lib/python3.10/abc.py:123: in __subclasscheck__
    return _abc_subclasscheck(cls, subclass)

We are using a config setup like the following (simple reproduction):

from pydantic_settings import BaseSettings

class BaseConfig(BaseSettings):
    pass

class Exclusion(BaseConfig):
    name: str = "*"

class Wrapper(BaseConfig):
    exclude: list[Exclusion] = []

class MyConfig(BaseConfig):
    coverage: Wrapper = Wrapper()

cfg = MyConfig()

^ When I run the above script, I basically get the same error as ours. I tried to make it as simple as possible.

[shedar]

I'm having the same issue with python3.10 and pydantic_settings 2.5.0. This line fails for any list[XXX] fields, since

>>> from pydantic.root_model import RootModel

>>> isinstance(list[int], type)
True

>>> issubclass(list[int], RootModel)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Cellar/python@3.10/3.10.14/Frameworks/Python.framework/Versions/3.10/lib/python3.10/abc.py", line 123, in __subclasscheck__
    return _abc_subclasscheck(cls, subclass)
TypeError: issubclass() arg 1 must be a class

[hramezani]

Thanks for reporting this issue. I try to fix the problem and prepare a new release soon.

[hramezani]

Just made a quick fix #392

Can you confirm that the fix is correct?

[shedar]

I can confirm that it works on my config.
But I don't fully understand the condition, so I don't know if this change has any undesired side effects.

[hramezani]

Thanks @shedar for checking. It shouldn't effect other things.

I will wait until tomorrow and then will prepare a patch release.

[hramezani]

pydantic-settings 2.5.1 which contain the fix has been released. Thanks for reporting!

[pgiraud]

It looks like the simple example provided by @antazoey is still failing with pydantic-settings 2.5.1 and python 3.9 or 3.10.

[pgiraud]

The example can even be simplified to:

from pydantic_settings import BaseSettings

class Bar(BaseSettings):
    foo: list[str] = []

cfg = Bar()

This fails with TypeError: issubclass() arg 1 must be a class error on 3.9 and 3.10.

[hramezani]

I created the second patch to fix the problem.
I keep the PR open for testing. Then will release a new patch.

Thanks all for reporting!

[hramezani]

pydantic-settings 2.5.2 has been released

[davidwaroquiers]

Thanks for this having looked at this quickly @hramezani. It also affected some of the software stack we are using. I will check if 2.5.2 indeed solves our issues. Maybe versions 2.5.0 and 2.5.1 could/should be yanked on pypi ?

[hramezani]

Thanks for this having looked at this quickly @hramezani. It also affected some of the software stack we are using. I will check if 2.5.2 indeed solves our issues. Maybe versions 2.5.0 and 2.5.1 could/should be yanked on pypi ?

Thanks @davidwaroquiers for confirming. I think we don't need to yank the previous version

[davidwaroquiers]

Hi @hramezani,

Seems that 2.5.2 indeed solves our issues.

Thanks again,

Best,

David

[antazoey]

Confirmed 2.5.2 fixed it for us.

[hramezani]

Thasnk all for reporting and helping to resolve the bug.