Sure, it only affects you. The problem is that changes to superclass can now break your code. For example, perhaps right now the function looks like this:

Sure, it only affects you. The problem is that changes to superclass can now break your code. For example, perhaps right now the function looks like this: def get(self, url, method='GET'): ... def post(self, url): self.get(url, method='POST') You override get, to add some additional functionality. All is fine. Then somebody realizes that the original code was silly, and rewrites it: def get(self, url, method='GET'): if method != 'GET': print "DEPRECATED!" self.request(url, method=method) def post(self, url): self.request(url, method='POST') It seems to do the same thing, and probably passes all the same tests. But suddenly, now your code doesn't get called for post requests and your additional functionality breaks in a mysterious way. Perhaps its still your fault for doing a bad job subclassing, but its going to look like its the fault of the person who fixed the parent class.