code: def show(self, exclude=[]):
          
          ordering = self.constant_keys + self.varying_keys
          spec_lines = [', '.join(['%s=%s' % (k, s[k]) for k in ordering
                                   if (k in s) and (k not in exclude)])
                        for s in self.specs]
          print('\n'.join(['%d: %s' % (i,l) for (i,l) in enumerate(spec_lines)]))
docs: Convenience method to inspect the available argument values in
          human-readable format. The ordering of keys is determined by
          how quickly they vary.
  
          The exclude list allows specific keys to be excluded for
          readability (e.g. to hide long, absolute filenames).