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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 getFilename(self,signature):
 """Returns the name of the output mask file that should reside on disk for the given signature. """


        filename=constructFilename(signature)

        if(fileutil.checkFileExists(filename)):
            return filename
        else:
            print("\nmMask file for ", str(signature), " does not exist on disk", file=sys.stderr)
            return None