code: def validate(self, fn):
          
          if self.duration[1] < 1:
              return
          created = dt.fromtimestamp(os.path.getctime(fn))
          d = {self.duration[0]: self.duration[1]}
          expired = created+timedelta(**d)
          if expired < dt.now():
              log.debug('%s expired, deleted', fn)
              os.remove(fn)
docs: Validate that the file has not expired based on the I{duration}.
          @param fn: The file name.
          @type fn: str