code: def transform(self, transform, desc=None):
          
          if desc is None:
              desc = u'transform({})'.format(getattr(transform, '__name__', ''))
  
          return self.replace(
              transforms=self.transforms + [transform],
              desc_stack=self.desc_stack + [desc]
          )
docs: Create a copy of this query, transformed by `transform`.
  
          Args:
              transform (callable): Callable that takes an iterable of values and
                  returns an iterable of transformed values.
  
          Keyword Args:
              desc (str): A description of the transform, to use in log messages.
                  Defaults to the name of the `transform` function.
  
          Returns:
              Query