AttributeError: __qualname__ on Python 3.9 with typing.Sequence, Collection, Iterable or other generic aliases

[palotasb]

To reproduce:

$ python3.9 -c 'from pydantic_settings import BaseSettings, CliSettingsSource
from typing import *
class S(BaseSettings):
    s: Sequence[int]  # or Collection, Iterable, etc.
CliSettingsSource(S)'

Traceback (most recent call last):
  File "<string>", line 5, in <module>
  File "/.../.venv/lib/python3.9/site-packages/pydantic_settings/sources.py", line 1165, in __init__
    self._connect_root_parser(
  File "/.../.venv/lib/python3.9/site-packages/pydantic_settings/sources.py", line 1574, in _connect_root_parser
    self._add_parser_args(
  File "/.../.venv/lib/python3.9/site-packages/pydantic_settings/sources.py", line 1656, in _add_parser_args
    kwargs['metavar'] = self._metavar_format(field_info.annotation)
  File "/.../.venv/lib/python3.9/site-packages/pydantic_settings/sources.py", line 1886, in _metavar_format
    return self._metavar_format_recurse(obj).replace(', ', ',')
  File "/.../.venv/lib/python3.9/site-packages/pydantic_settings/sources.py", line 1874, in _metavar_format_recurse
    list(map(self._metavar_format_recurse, self._get_modified_args(obj))), obj_qualname=obj.__qualname__
  File "/opt/homebrew/Cellar/python@3.9/3.9.20/Frameworks/Python.framework/Versions/3.9/lib/python3.9/typing.py", line 711, in __getattr__
    raise AttributeError(attr)
AttributeError: __qualname__

The error also happens when using types based on typing._BaseGenericAlias, like typing.Collection or typing.Iterable

The call ultimately fails on this line:
https://github.com/python/cpython/blob/3.9/Lib/typing.py#L711

The support for .__qualname__ for generic aliases was added only in Python 3.10:
https://github.com/python/cpython/blob/3.10/Lib/typing.py#L977

Hence this call on Python 3.9 is wrong:
https://github.com/pydantic/pydantic-settings/blob/v2.6.1/pydantic_settings/sources.py#L1874

[palotasb]

Somehow pydantic~=2.10.0 is causing this break.

uv run --isolated --no-project --with pydantic-settings --with pydantic==2.10.0 --python python3.9 - <<EOF
from pydantic_settings import BaseSettings, CliSettingsSource
from typing import *
class S(BaseSettings):
    s: Sequence[int]  # or Collection, Iterable, etc.
CliSettingsSource(S)
print("success")
EOF

Results in:

Traceback (most recent call last):
  File "<string>", line 5, in <module>
  File "/.../lib/python3.9/site-packages/pydantic_settings/sources.py", line 1165, in __init__
    self._connect_root_parser(
  File "/.../lib/python3.9/site-packages/pydantic_settings/sources.py", line 1574, in _connect_root_parser
    self._add_parser_args(
  File "/.../lib/python3.9/site-packages/pydantic_settings/sources.py", line 1656, in _add_parser_args
    kwargs['metavar'] = self._metavar_format(field_info.annotation)
  File "/.../lib/python3.9/site-packages/pydantic_settings/sources.py", line 1886, in _metavar_format
    return self._metavar_format_recurse(obj).replace(', ', ',')
  File "/.../lib/python3.9/site-packages/pydantic_settings/sources.py", line 1874, in _metavar_format_recurse
    list(map(self._metavar_format_recurse, self._get_modified_args(obj))), obj_qualname=obj.__qualname__
  File "/opt/homebrew/Cellar/python@3.9/3.9.20/Frameworks/Python.framework/Versions/3.9/lib/python3.9/typing.py", line 711, in __getattr__
    raise AttributeError(attr)
AttributeError: __qualname__

But:

uv run --isolated --no-project --with pydantic-settings --with pydantic~=2.9.0 --python python3.9 - <<EOF
from pydantic_settings import BaseSettings, CliSettingsSource
from typing import *
class S(BaseSettings):
    s: Sequence[int]  # or Collection, Iterable, etc.
CliSettingsSource(S)
print("success")
EOF

Prints:

success

[hramezani]

Thanks @palotasb for reporting this issue. I could reproduce it.

question: what do you want to achieve by CliSettingsSource(S)?

[palotasb]

That line creates an instance of class CliSettingsSource and then immediately throws it away, just to demonstrate this bug.

The code I shared is just a minimal reproducible example for a more complex bug that we encountered in our internal codebase. The original code is proprietary so I can't share it, but this smaller example also makes it easier to identify and fix the underlying issue.

In our real codebase class S(BaseSettings): ... is a much more complex class where only one of the fields is a generic alias. Also in our case cli_settings_source = CliSettingSource(S) is not just initialized and thrown away, but instead it's assigned to a variable and used later on to do something useful.

[hramezani]

@palotasb Thanks for your reply. Yes, it is related to a change in Pydantic. we have some custom logic ported from Pydantic.

I created #497 to fix the problem.
Could you please test it?