<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def cast_config(cls, config: typing.Mapping[str, str]) -> typing.Dict[str, str]: """Cast `config` to grouped regular expressions."""

        return {k: cls.cast(v, k) for k, v in config.items()}