Python application configuration via the environment
Envier is a Python library for extracting configuration from environment variables in a declarative and (eventually) 12-factor-app-compliant way.
The following example shows how to declare the configuration for an application
that uses the MYAPP_DEBUG
, MYAPP_SERVICE_HOST
and MYAPP_SERVICE_PORT
variables from the environment.
>>> from envier import Env
>>>
>>> class GlobalConfig(Env):
>>> __prefix__ = "myapp"
>>>
>>> debug_mode = Env.var(bool, "debug", default=False)
>>>
>>> service_host = Env.var(str, "service.host", default="localhost")
>>> service_port = Env.var(int, "service.port", default=3000)
>>>
>>> _is_default_port = Env.der(bool, lambda c: c.service_port == c.spec.service_port.default)
>>>
>>> config = GlobalConfig()
>>> config.service_port
3000
>>> config._is_default_port
True
Configurations can also be nested to create namespaces:
>>> from envier import Env
>>>
>>> class ServiceConfig(Env):
>>> __prefix__ = "service"
>>>
>>> host = Env.var(str, "host", default="localhost")
>>> port = Env.var(int, "port", default=3000)
>>>
>>> class GlobalConfig(Env):
>>> __prefix__ = "myapp"
>>>
>>> debug_mode = Env.var(bool, "debug", default=False)
>>>
>>> service = ServiceConfig
>>>
>>> config = GlobalConfig()
>>> config.service.port
3000
The same configuration can be obtained with implicit nesting by declaring the
ServiceConfig
subclass inside GlobalConfig
, and setting the class attribute
__item__
to the name of the item the sub-configuration should be assigned to,
viz.
>>> from envier import Env
>>>
>>> class GlobalConfig(Env):
>>> __prefix__ = "myapp"
>>>
>>> debug_mode = Env.var(bool, "debug", default=False)
>>>
>>> class ServiceConfig(Env):
>>> __item__ = __prefix__ = "service"
>>>
>>> host = Env.var(str, "host", default="localhost")
>>> port = Env.var(int, "port", default=3000)
>>>
>>> config = GlobalConfig()
>>> config.service.port
3000
The library ships with a mypy
plugin to allow for type checking. If you want
to use it, either install the library with the mypy
extra or ensure that
mypy
is installed, and then add envier.mypy
to the list of extra plugins in
the mypy
configuration.