API

class twelvefactor.Config(environ=None)

Bases: object

Config environment parser.

This class allows chosen configuration values to be extracted from the processes environment variables and converted into the relevant types.

parser = Config()

config = parser({
    'DEBUG': {
        'type': bool,
        'default': False,
    },
    'SECRET_KEY': str,
})

The above will populate the config variable with two values, DEBUG will be populated with a bool from the environment variable of the same name, throwing an exception on invalid values and defaulting to False when none is provided, and SECRET_KEY will be a str and throw a ConfigError when no value is found in the environment.

An optional environ param can be passed in order to override the environment.

Parameters

environ (Optional[Mapping[str, str]]) – environment dictionary, defaults to os.environ

__call__(schema)

Parse the environment according to a schema.

Parameters

schema (Mapping[str, Union[Type[Any], SchemaItem]]) – the schema to parse

Return type

Dict[str, Any]

Returns

a dictionary of config values

get(key, default=<object object>, type_=<class 'str'>, subtype=<class 'str'>, mapper=None)

Parse a value from an environment variable.

>>> os.environ['FOO']
<<< '12345'
>>>
>>> os.environ['BAR']
<<< '1,2,3,4'
>>>
>>> 'BAZ' in os.environ
<<< False
>>>
>>> parser = Config()
>>> parser.get('FOO', type_=int)
<<< 12345
>>>
>>> parser.get('BAR', type_=list, subtype=int)
<<< [1, 2, 3, 4]
>>>
>>> parser.get('BAZ', default='abc123')
<<< 'abc123'
>>>
>>> parser.get('FOO', type_=int, mapper=lambda x: x*10)
<<< 123450

Parameters

• key (str) – the key to look up the value under

• default (Any) – default value to return when when no value is present

• type_ (Type[Any]) – the type to return

• subtype (Type[Any]) – subtype for iterator types

• mapper (Optional[Callable[[object], object]]) – a function to post-process the value with

Return type

Any

Returns

the parsed config value

parse(value, type_=<class 'str'>, subtype=<class 'str'>)

Parse value from string.

Convert value to

>>> parser = Config()
>>> parser.parse('12345', type_=int)
<<< 12345
>>>
>>> parser.parse('1,2,3,4', type_=list, subtype=int)
<<< [1, 2, 3, 4]

Parameters

• value (str) – string

• type_ (Type[Any]) – the type to return

• subtype (Type[Any]) – subtype for iterator types

Return type

Any

Returns

the parsed config value

class twelvefactor.ConfigError

Bases: Exception

Exception to throw on configuration errors.

twelvefactor.SchemaItem

A type annotation for the definition of a single item in a the schema.

twelvefactor.Schema

A type annotation for the Schema.

twelvefactor.config

An instance of Config.