Walter

Walter is a configuration library, inspired by python-decouple, and intended to replace direct access to os.environ in Django settings.py files (although it is by no means Django-specific). It currently supports Python 3.6+.

It differs from other, similar libraries for one reason: when your users try to start up your app with invalid configuration, the error message they get shows a list of all of the errors with every configuration parameter, not just the first one.

Installation

pip install walter
# or
poetry add walter

Usage

Here's an example of a Python file that uses Walter to define its configuration.

from walter import Config

with Config(author="Acme Inc.", name="My Awesome App") as config:

    # Read a configuration value with config()
    SECRET_KEY = config('SECRET_KEY')

    # Convert the returned value to something other than a string with cast.
    DEBUG = config('DEBUG', cast=bool)

    # You can pass any function that takes a string to `cast`.
    # Here, we're using a third party function to parse a database URL
    # string into a Django-compatible dictionary.
    import dj_database_url
    DATABASES = {
        'default': config('DATABASE_URL', cast=dj_database_url.parse),
    }

    # You can also make a parameter optional by giving it a default.
    SENTRY_DSN = config('SENTRY_DSN', default=None)

print(f"Here, you can use values like {SITE_NAME}!")

If we run that code without setting anything, Walter throws an error at the end of the with block.

Traceback (most recent call last):
File "<stdin>", line 27, in <module>
File "/Users/leigh/Projects/walter/walter/config.py", line 90, in __exit__
    raise ConfigErrors(errors=self.errors)
walter.config.ConfigErrors: 4 configuration values not set, 0 invalid

SECRET_KEY not set
DEBUG not set
DATABASE_URL not set
SITE_NAME not set

Note that Walter lists out all of the errors in our configuration, not just the first one! If we set all of those settings as environment variables and run the code again, the code runs to completion:

Here, you can use values like MyAwesomeApp!