def from_envvar(self, variable_name):
config_file = os.environ.get(variable_name)<EOL>if not config_file:<EOL><INDENT>raise RuntimeError('<STR_LIT>'<EOL>'<STR_LIT>' %<EOL>variable_name)<EOL><DEDENT>return self.from_pyfile(config_file)<EOL>
Load a configuration from an environment variable pointing to
        a configuration file.

        :param variable_name: name of the environment variable
        :return: bool. ``True`` if able to load config, ``False`` otherwise.