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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 file():
 """ Grammar for files found in the overall input files.	"""

        return (
            Optional(Word(alphanums).setResultsName('alias') +
                Suppress(Literal('.'))) + Suppress(White()) +
            Word(approved_printables).setResultsName('filename')
            )