code: def delete_property(self, key):
          
          if key in self.RESERVED_ATTRIBUTE_NAMES:
              raise KeyError(key)
          del self.o[key]
docs: Remove a property from the document.
  
          Calling code should use this method to remove properties on the
          document instead of modifying ``properties`` directly.
  
          If there is a property with the name in ``key``, it will be removed.
          Otherwise, a ``KeyError`` will be thrown.