Add support for conversion from str in pydantic-settings

[BartSchuurmans]

from pathlib import Path
from upath import UPath
from pydantic_settings import BaseSettings

class Settings(BaseSettings):
    my_path: Path
    my_upath: UPath

settings = Settings(my_path="/tmp", my_upath="/tmp")

❯ python example.py
Traceback (most recent call last):
  File "/home/bart/src/proj/example.py", line 9, in <module>
    settings = Settings(my_path="/tmp", my_upath="/tmp")
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/bart/src/proj/.venv/lib/python3.12/site-packages/pydantic_settings/main.py", line 152, in __init__
    super().__init__(
  File "/home/bart/src/proj/.venv/lib/python3.12/site-packages/pydantic/main.py", line 212, in __init__
    validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.ValidationError: 1 validation error for Settings
my_upath
  Input should be an instance of UPath [type=is_instance_of, input_value='/tmp', input_type=str]
    For further information visit https://errors.pydantic.dev/2.9/v/is_instance_of

When reading through some older (solved) issues, I got the impression that this used to work. Should this work out of the box?

pydantic                  2.9.2          Data validation using Python type ...
pydantic-core             2.23.4         Core functionality for Pydantic va...
pydantic-settings         2.5.2          Settings management using Pydantic
universal-pathlib         0.2.5          pathlib api extended to use fsspec...

[ap--]

Hi @BartSchuurmans

Regarding the implementation, imo behavior here is correct. This only works for your pathlib.Path attributes because of lax mode: https://docs.pydantic.dev/latest/concepts/conversion_table/#__tabbed_1_1

See:

>>> from pathlib import Path
... from pydantic import ConfigDict
... from pydantic_settings import BaseSettings
... 
>>> class Settings(BaseSettings):
...     model_config = ConfigDict(strict=True)
...     my_path: Path
...     
>>> Settings(my_path="/tmp")
Traceback (most recent call last):
  File "<python-input-4>", line 1, in <module>
    Settings(my_path="/tmp")
    ~~~~~~~~^^^^^^^^^^^^^^^^
  File "/Users/andreaspoehlmann/Development/universal_pathlib/venv313/lib/python3.13/site-packages/pydantic_settings/main.py", line 144, in __init__
    super().__init__(
    ~~~~~~~~~~~~~~~~^
        **__pydantic_self__._settings_build_values(
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<20 lines>...
        )
        ^
    )
    ^
  File "/Users/andreaspoehlmann/Development/universal_pathlib/venv313/lib/python3.13/site-packages/pydantic/main.py", line 211, in __init__
    validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
pydantic_core._pydantic_core.ValidationError: 1 validation error for Settings
my_path
  Input should be an instance of Path [type=is_instance_of, input_value='/tmp', input_type=str]
    For further information visit https://errors.pydantic.dev/2.9/v/is_instance_of

I can see how users would expect to be able to just cast from string by default though. You can do this right now via: https://docs.pydantic.dev/latest/concepts/validators/#before-after-wrap-and-plain-validators . But I agree, that this should be more convenient. We should make sure to expose storage_options in some way to pydantic too.

[BartSchuurmans]

@ap-- Thanks for your quick response!

I am using the PlainValidator now to support converting str to UPath:

from typing import Annotated
from pydantic import PlainValidator
from upath import UPath
from pydantic_settings import BaseSettings

class Settings(BaseSettings):
    my_upath: Annotated[UPath, PlainValidator(lambda x: UPath(x))]

settings = Settings(my_upath="/tmp")