How to use yaml_file parameter for pydantic settings

Question

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?

strawdog · Accepted Answer · 2025-07-31 10:59:17Z

2

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:

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)

edited Jul 31 at 10:59

answered Jul 30 at 7:26

strawdog

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4 Comments

Kraigolas Jul 30 at 7:30

"I found easier customize sources like this" actually this seems to be exactly what they state to do in the docs. Feel free to link these in answer :)

rzlvmp Jul 31 at 1:56

Unfortunately documentation do not provide any information what are some restrictions :( And do not describe that yaml_file parameter makes sense only if settings_customise_sources method is overridden. Anyway, my code will be completely working if you add return (YamlConfigSettingsSource(settings_cls),) without providing c.yaml as argument (all yaml parameters will be taken from model_config). If you would like to update your answer using model_config I will mark it as correct (since my question is about how to use yaml related arguments)

[deleted]

rzlvmp Jul 31 at 10:34

Just one moment: to read sectioned parameters, extra="allow" argument is obligatory → extra is needed here because you simply didn't add port: int field into Settings class. So port: 123 is an extra parameter for the class. It is completely not related to sectioned parameters

strawdog Jul 31 at 11:01

@rzlvmp well, fair. fixed.

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