os-env-injection 0.0.0

Utilities to handle OS environment variables

os-env

Utilities to handle OS environment variables

Why this library?

You have a function which requires several arguments that typically depend on the system on when the function is running

def f(url: str, user: str, password: str, subdomain: str):
    ...

You would like to have the possibility to have its values to be read from the OS env. If you simply do

import os

def f(
    url: str = os.environ["URL"],
    user: str = os.environ["USER"],
    password: str = os.environ["PASSWORD"],
    subdomain: str = os.environ["SUBDOMAIN"],
):
    ...

then you will encounter a problem whenever the OS env variables are not set, because the defaults are evaluated at import time. This means in practice, that you will be forced to use them, instead of passing the values directly.

A workaround is to write

import os

def f(
    url: str = os.environ.get("URL", None),
    user: str = os.environ.get("USER", None),
    password: str = os.environ.get("PASSWORD", None),
    subdomain: str = os.environ.get("SUBDOMAIN", None),
):
    ...

In this way, there are still a couple of drawbacks:

• it is necessary to write code to check the values of each variable to raise an exception if values are missing (None)
• the default values will be evaluated when the function is first imported.
  In case you are setting the OS env dynamically (e.g. by executing a shell script with exports) you could end up in troubles.

The nice solution - Quickstart

First, install the library

pip install os-env

From the previous example, say that all variables are required except for subdomain which can stay None. One can use this library to write:

from os_env import inject_os_env, OSEnvInjected
from typing import Optional

@inject_os_env(keymap={"url": "OS_ENV_URL", "user": "OS_ENV_USER", "password": "OS_ENV_PASSWORD"})
def f(url: OSEnvInjected, user: OSEnvInjected, password: OSEnvInjected, subdomain: Optional[OSEnvInjected]):
    ...

What will happen?

• If you explicitly pass a value when you call f, it will be used
• If no value is passed, then it will try to read it from the OS environment. It will look for the variable with name specified in the decorator, if given, otherwise the variable name itself. E.g. in our example, it will look into $OS_ENV_URL for the url value, and $subdomain for subdomain.
• If no value is found in the OS environment too, then it will raise an exception if the type is OSEnvInjected. It will not raise an exception and set the value to None if the type is Optional[OSEnvInjected].

Don't specify the OS env keys

It is possible to skip altogether the argument os_env_keymap in the decorator:

from os_env import inject_os_env, OSEnvInjected
from typing import Optional

@inject_os_env
def f(url: OSEnvInjected, 
      user: OSEnvInjected, 
      password: OSEnvInjected, 
      subdomain: Optional[OSEnvInjected]):
    ...

In this case, the OS environment variables will be $url, $user, $password, and $subdomain.

Setup development environment (for contributors only)

• Create a virtual environment and activate it

  python -m venv venv
  source venv/bin/activate
  

• Install the developer dependencies you will need

  pip install -U pip wheel setuptools
  pip install -e .[dev]
  

• Set black as pre-commit package (will automatically apply black before committing)

  pre-commit install
  

• To run the tests

  pytest