code: def convert(self, value, param, ctx):
          
          if not isinstance(value, tuple):
              parsed = urlparse.urlparse(value)
              if parsed.scheme not in ('telnet', 'ssh'):
                  self.fail('invalid URL scheme (%s).  Only telnet and ssh URLs are '
                            'allowed' % parsed, param, ctx)
          return value
docs: Convert to URL scheme.