When writing 12-factor applications, we often need to write lengthy, tedious code for parsing environment variables.
Dozen is a simple, declarative library for mapping environment variables to configuration types.
>>> import dozen >>> import os >>> >>> # Given some variables in the environment >>> os.environ.update({ >>> 'USE_ENVIRONMENT': 'true', >>> 'SOME_STRING': 'my value', >>> 'PORT': '2345' >>> }) >>> >>> # ... and a template for our config >>> class MyConfig(dozen.Template): >>> use_environment: bool >>> some_string: str >>> port: int >>> >>> # dozen returns populated instances of our template from env vars >>> cfg = MyConfig.build() >>> assert cfg.use_environment is True >>> assert cfg.some_string == 'my value' >>> assert cfg.port == 2345
Sometimes we want to treat a value as optional, and give it a default value.
>>> os.environ.clear() >>> >>> class DefaultConfig(dozen.Template): >>> use_environment: bool = True >>> some_string: str = "cheese" >>> some_optional_string: str = None >>> port: int = 73 >>> >>> cfg = DefaultConfig.build(env=dict()) >>> assert cfg.use_environment is True >>> assert cfg.some_string == 'cheese' >>> assert cfg.port == 73
For backing services, we often want to set addresses as env vars
>>> import dozen >>> import os >>> >>> # Given some variables in the environment >>> os.environ.update({ >>> 'MYAPP_WEB_HOST': 'app.example.org', >>> 'MYAPP_WEB_PORT': '8080', >>> }) >>> >>> # ... and a template for our config >>> class MyConfig(dozen.Template): >>> web: dozen.service() >>> api: dozen.service(default_host='api.example.org', default_port=9000) >>> >>> # dozen returns populated instances of our template from env vars >>> cfg = MyConfig.build(prefix='myapp') >>> assert cfg.web.host == 'app.example.org' >>> assert cfg.web.port == 8080 >>> assert cfg.api.host == 'api.example.org' >>> assert cfg.api.port == 9000