Prevent code to be re-executed with auto-reload enabled

[AndreuCodina]

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Example Code

# application_settings.py
from pydantic_settings import BaseSettings
class ApplicationSettings(BaseSettings):
  field: str


# dependency_container.py
class DependencyContainer:
  @classmethod
  def initialize(cls) -> None:
    self.application_settings = ApplicationSettings(field="value")


# main.py
DependencyContainer.initialize()
app = FastAPI(title="Demo", version="1.0.0")

Description

We read the configurations and secrets from Azure Key Vault (https://github.com/pydantic/pydantic-settings/blob/main/docs/index.md#azure-key-vault) and Azure App Configurations (https://github.com/AndreuCodina/pydantic-settings-azure-app-configuration) when FastAPI is executed with auto-reload and we store them in a BaseSettings class (from the pydantic-settings package). In summary, we instantiate a singleton of that class.

When a piece of code is changed, the auto-reload executes main.py again and the singleton is re-instantiated. Each reading costs money and takes time, so we need to not re-execute the singleton instantiation when FastAPI detects a change.

Operating System

Linux, Windows, macOS

Operating System Details

Latest.

Python Version

3.12.4

Additional Context

No response

[j-carson]

If that line is not re-executed, then your singleton won't be initialized at all.

If you can test and develop some functions without that singleton, I suggest changing your class to not execute the costly code until the first access of azure services is needed. You could also control this by having separate dev and production development environments where developers do not need to go to azure every time they save a code change.