How to use yaml_file parameter for pydantic settings

Here is my example code:

from pathlib import Path
from pydantic_settings import BaseSettings, SettingsConfigDict

class Settings(BaseSettings):
    model_config = SettingsConfigDict(
        yaml_file=Path('c.yaml'),
        yaml_config_section='blah',
    )

    port: int


s = Settings()

and my c.yaml stored in the same directory:

blah:
  port: 123

When I'm running Python file I'm getting message:

pydantic_core._pydantic_core.ValidationError: 1 validation error for Settings
port
  Field required [type=missing, input_value={}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.11/v/missing

That means that Pydantic isn't even trying to read YAML file. I found multiple answers how to read YAML and most of it is about how to read YAML, convert it to dict and pass the dict as constructor arguments. But I could not find any information why this yaml_file and yaml_config_section exists and what it does.

Is here a simple way to read YAML using these arguments?

Due some restrictions Pydantic has in direct reading of YAML files, I found it easier to customize sources like this (as per documentation):

from pydantic import BaseModel
from pydantic_settings import BaseSettings, YamlConfigSettingsSource

# Nothe the model declaration for your section
class BlahSettings(BaseModel):
    port: int

class Settings(BaseSettings):
    blah: BlahSettings
    @classmethod
    def settings_customise_sources(cls, settings_cls, **kwargs):
        return (YamlConfigSettingsSource(settings_cls, "c.yaml"),)

s = Settings()
print(s.blah.port)

which, hopefully, gives:

123

UPDATE

as OP mentioned in the conmment, it was possible to use model_config along with overridden method settings_customise_sources without explicit use of yaml_file parameter, which would be taken from the model_config itself.

from pydantic_settings import BaseSettings, YamlConfigSettingsSource, SettingsConfigDict

class Settings(BaseSettings):
    port: int
    model_config = SettingsConfigDict(
        yaml_file='c.yaml',
        yaml_config_section='blah',
        )
    @classmethod
    def settings_customise_sources(cls, settings_cls, **kwargs):
        return (YamlConfigSettingsSource(settings_cls),)



s = Settings()
print(s.port)