def __str__(self) : #Check the outfile, filter, or stdout option has been set. #We can't simply do this via the required flag for the outfile #output - this seems the simplest solution. if not (self.outfile or self.filter or self.stdout) : raise ValueError("You must either set outfile (output filename), " "or enable filter or stdout (output to stdout).") return AbstractCommandline.__str__(self)