code: def change_content_type(self, new_ctype, guess=False):
          
          self.container.change_object_content_type(self, new_ctype=new_ctype,
                  guess=guess)
docs: Copies object to itself, but applies a new content-type. The guess
          feature requires the container to be CDN-enabled. If not then the
          content-type must be supplied. If using guess with a CDN-enabled
          container, new_ctype can be set to None.
          Failure during the put will result in a swift exception.