@David Maze Thanks for the response, I am not fully understanding how this works. Can you give me some more advice?

For more context I am using a streamlit app.

Here's what I am trying:

1. Remove code, settings = Settings() remove from settings.py

2. Add code settings = Settings() to config.py

3. Make modules import from config from .config import settings

This will make sure settings are declared once, prevent side effects of Settings() being ran every time I import settings.py, and I can patch it in Pytest.

So here would be the the new implementation based on what you said...

# settings.py
from pydantic_settings import BaseSettings, SettingsConfigDict
from pydantic import Field

class Settings(BaseSettings):
    model_config = SettingsConfigDict(
        env_file=".env",
    )

    env_var: str = Field(description="blah blah blah")
    # ...
    env_var_d: str = Field(description="blah blah blah")

# config.py
from .settings import Settings

def get_settings()
    return Settings()

# some_module.py
from .config import get_settings

def some_func()
    settings = get_settings()

# conftest.py
import pytest
from .settings import Settings
from unittest.mock import patch

# Does not work as expected
@pytest.fixture(autouse=True, scope="session")
def settings():
    with patch('pckg.config.get_settings', Settings(_env_file=".env.test")):
        yield