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
Returns the name of the output mask file that
        should reside on disk for the given signature.