code: def source_file(pymux, variables):
      
      filename = os.path.expanduser(variables['<filename>'])
      try:
          with open(filename, 'rb') as f:
              for line in f:
                  line = line.decode('utf-8')
                  handle_command(pymux, line)
      except IOError as e:
          raise CommandException('IOError: %s' % (e, ))
docs: Source configuration file.