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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 _filename(self, ifo, description, extension, segment):
 """ Construct the standard output filename. Should only be used internally of the File class. """

        if extension.startswith('.'):
            extension = extension[1:]

        # Follow the frame convention of using integer filenames,
        # but stretching to cover partially covered seconds.
        start = int(segment[0])
        end = int(math.ceil(segment[1]))
        duration = str(end-start)
        start = str(start)

        return "%s-%s-%s-%s.%s" % (ifo, description.upper(), start,
                                   duration, extension)