code: def set_property(self, key, value):
          
          if key in self.RESERVED_ATTRIBUTE_NAMES:
              return
          self.o[key] = value
docs: Set a property on the document.
  
          Calling code should use this method to add and modify properties
          on the document instead of modifying ``properties`` directly.
  
          If ``key`` is ``"_links"`` or ``"_embedded"`` this method will silently
          fail.
  
          If there is no property with the name in ``key``, a new property is
          created with the name from ``key`` and the value from ``value``. If
          the document already has a property with that name, it's value
          is replaced with the value in ``value``.