code: def last_modified(self):
          '''Read the last-modified header as a datetime, if present.'''
          lm = self.response.headers.get('last-modified', None)
          return datetime.strptime(lm, '%a, %d %b %Y %H:%M:%S GMT') if lm \
              else Nonf last_modified(self):
          '''Read the last-modified header as a datetime, if present.'''
          lm = self.response.headers.get('last-modified', None)
          return datetime.strptime(lm, '%a, %d %b %Y %H:%M:%S GMT') if lm \
              else None
docs: Read the last-modified header as a datetime, if present.