SettingsReader.py

class SettingsReader:
    def __init__(self, opts, config, settings):
        self.opts = opts
        self.config = config
        self.settings = settings

    def __contains__(self, key):
        if (key in self.opts  or
            key in self.config or
            key in self.settings):
            return True
        return False

    def __getitem__(self, key):
        if key in self.opts:
            value = self.opts.get(key)
        elif key in self.config:
            value = self.config.get(key)
        elif key in self.settings:
            value = self.settings.get(key)
        else:
            raise MissingParamException('Missing ' + param_name)
        return value

    def get(self, key, function=lambda: None):
        try:
            return self[key]
        except MissingParamException:
            pass

        return function()