<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def delete_key(self, key_id):
 """Delete user key pointed to by ``key_id``. :param int key_id: (required), unique id used by Github :returns: bool """

        key = self.key(key_id)
        if key:
            return key.delete()
        return False