code: def has(self, block, name):
          
          try:
              self.get(block, name)
              return True
          except KeyError:
              return False
docs: Return whether or not the field named `name` has a non-default value for the XBlock `block`.
  
          :param block: block to check
          :type block: :class:`~xblock.core.XBlock`
          :param name: field name
          :type name: str