Example code for wrapping os.environ.get()

envi.py

"""get_envi module

Consistently retrieve environment variables to use in your modules.

Try-it-out with:

    `python -m pytest envi.py`

"""

from os import environ

import pytest


def is_true(env_str):
    return env_str.lower() in ["true", "yes", "on", "1"]


def get_envvar(name, default, cast=False):
    """Wraps os.environ.get to manage type consistency.

    :param name: environment variable name to get.
    :param default: default to use when name can't be got.
    :param cast: python type to cast the return value to, e.g. when the
            plain-string is just fine.
    """
    if not cast:
        return environ.get(name, default)
    envvar = environ.get(name, default)
    if cast == bool:
        return is_true(envvar)
    try:
        return cast(envvar)
    except ValueError:
        return default


@pytest.mark.parametrize(
    "return_value, default, cast, expected_result",
    [
        # Return True correctly.
        ("true", "False", bool, True),
        # Return False correctly.
        ("not true", "", bool, False),
        # Return a plain-string.
        ("some_setting", "", None, "some_setting"),
        # Return a properly cast int.
        (1, "2", int, 1),
        # Return the default for a ValueError for an int.
        ("string", 42, int, 42),
        # etc.
    ],
)
def test_get_envvar(return_value, default, cast, expected_result, mocker):
    """Test various different environment return values"""

    if cast is None:
        mock = mocker.patch("os.environ.get", return_value=return_value)
        assert get_envvar("value", "") == expected_result
    else:
        mock = mocker.patch("os.environ.get", return_value=return_value)
        assert get_envvar("value", default, cast) is expected_result

    assert mock.called_once()