from classyconf import Configuration, Value, Environment, IniFile, as_boolean, EnvPrefix

class AppConfig(Configuration):
    """Configuration for My App"""
    class Meta:
        loaders = [
            Environment(keyfmt=EnvPrefix("MY_APP_")),
            IniFile("/etc/app/conf.ini", section="myapp")
        ]

    DEBUG = Value(default=False, cast=as_boolean, help="Toggle debugging mode.")
    DATABASE_URL = Value(default="postgres://localhost:5432/mydb", help="Database connection.")

>>> config = AppConfig()
>>> print(config)
DEBUG=True - Toggle debugging mode.
DATABASE_URL='postgres://localhost:5432/mydb' - Database connection.

>>> config = AppConfig()
>>> config
AppConf(loaders=[Environment(keyfmt=EnvPrefix("MY_APP_"), EnvFile("main.env")])

class TestConfig(AppConfig):
    class Meta:
        loaders = [IniFile("test_settings.ini"), EnvFile("main.env")]

>>> dev_config = AppConfig(loaders=[IniFile("dev_settings.ini")])
>>> dev_config.DEBUG
True

>>> config.DEBUG
False
>>> config["DEBUG"]
False

 >>> for setting in config:
...     print(setting)
...
('DEBUG', Value(key="DEBUG", help="Toggle debugging on/off."))
('DATABASE_URL', Value(key="DATABASE_URL", help="Database connection."))

def do_something(cfg):
    if cfg.DEBUG:   # this is evaluated lazily
         return