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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def retry_after(cls, response, default=5, _now=time.time):
 """ Parse the Retry-After value from a response. """

        val = response.headers.getRawHeaders(b'retry-after', [default])[0]
        try:
            return int(val)
        except ValueError:
            return http.stringToDatetime(val) - _now()