Op 29-09-15 om 13:17 schreef Anssi Saari: > Antoon Pardon <antoon.par...@rece.vub.ac.be> writes: > >> Op 29-09-15 om 11:27 schreef ple...@gmail.com: >>> I have a perplexing problem with Python 3 class variables. I wish to >>> generate an unique ID each time an instance of GameClass is >>> created. There are two versions of the __gen_id method with test run >>> results for each listed below the code. >> The problem is that in python you can't change a class variable through an >> instance. The moment you >> try, you create an instance attribute. > That much is clear but why does his other version of __gen_id() work > (after a fashion)? It doesn't increment the class variable but the > instances get an incremental id. > > The function was like this: > > def __gen_id(self): > ty = self.__class__.__name__ > id = '' > while id in self.__instance_registry: > id = '%s_%d' % (ty, self.__instance_counter) > self.__instance_counter += 1 > self.__instance_registry[id] = self > return id
Because you check against the class variable __instance_registry. That variable isn't rebound, it is mutated, so it remains a class variable and can thus be used to check which id's are already in use. So you increment your counter until the corresponding id is not in the __instance_registry. -- Antoon Pardon. -- https://mail.python.org/mailman/listinfo/python-list
