metaclass with dynamic creation of properties

Meteclass with dynamic properties creation: Written as helper class for my graph implementation (metaclass for nodes, edges and graph itself).

yet another Observer pattern in python

Observer sniffing a particular attribute from Observable class. This little spy is notified every time watched attribute is changing its value.

Observers are hold in weakref.WeakValueDictionary to avoid crashes in case they would disappear (i.e. being collected and deleted by gc). And here is the source code: