Key-Value Observing and Python ============================== Key-Value Coding and Key-Value Observing are supported by PyObjC. Key-Value Observing is only supported for Cocoa objects though, because it is technically impossible to generate the right events for pure python objects (such as ``dict`` or ``list`` instances). * _: at least not without patching the Python interpreter itself. PyObjC will automaticly call ``willChangeValueForKey:`` and ``didChangeValueForKey:`` when changing the attribute of an object that is a subclass of ``NSObject``. It is therefore not necessary to call those methods in most use-cases for Key-Value Observing. .. warning:: The 'change' dictionary for ``observeValueForKeyPath:ofObject:change:context:`` can be changed after the method call, don't store a reference to this dictionary but make a copy when you want to use its contents later on.