<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_retry_after(self, response):
 """ Get the value of Retry-After in seconds. """


        retry_after = response.getheader("Retry-After")

        if retry_after is None:
            return None

        return self.parse_retry_after(retry_after)