<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def expire_key(self, key):
        '''
        Expire the key, delete the value, and call the callback function
        if one is specified.

        Args:
            key: The ``TimedDict`` key
        '''
        value = self.base_dict[key]
        del self[key]
        if self.callback is not None:
            self.callback(
                key, value, *self.callback_args, **self.callback_kwargs)