def output_file(self):
        """
        If only one output file return it. Otherwise raise an exception.
        """
        out_files = self.output_files
        if len(out_files) != 1:
            err_msg = "output_file property is only valid if there is a single"
            err_msg += " output file. Here there are "
            err_msg += "%d output files." %(len(out_files))
            raise ValueError(err_msg)
        return out_files[0]
def output_file ( self ) : out_files = self . output_files if len ( out_files ) != 1 : err_msg = "output_file property is only valid if there is a single" err_msg += " output file. Here there are " err_msg += "%d output files." % ( len ( out_files ) ) raise ValueError ( err_msg ) return out_files [ 0 ]
If only one output file return it. Otherwise raise an exception.