code: def change_object_content_type(self, container, obj, new_ctype,
              guess=False):
          
          cname = utils.get_name(container)
          oname = utils.get_name(obj)
          if guess and container.cdn_enabled:
              # Test against the CDN url to guess the content-type.
              obj_url = "%s/%s" % (container.cdn_uri, oname)
              new_ctype = mimetypes.guess_type(obj_url)[0]
          return self.copy_object(container, obj, container,
                  content_type=new_ctype)
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 an exception.