On Thu, 21 Apr 2011 19:00:08 +0100, MRAB wrote: >>> How can HomeHandler call foo() when I never created an instance of >>> BaseHandler? >> >> But you created one! >> > No, he didn't, he created an instance of HomeHandler. > >> test is an instance of HomeHandler, which is a subclass of BaseHandler, >> so test is also an instance of BaseHandler. >> > test isn't really an instance of BaseHandler, it's an instance of > HomeHandler, which is a subclass of BaseHandler.
Which *also* makes it an instance of BaseHandler. You are a human being, which also makes you a mammal. It would be *wrong* to say that you're not a mammal, just because you're a human being. But to answer the Original Poster's question... you don't need a formal BaseHandler instance because that's how inheritance is designed to work. Each class knows its own parent classes, and when you call test.foo(), Python walks the chain of: instance instance's class each of the parent class(es) (if any) looking for a match for foo, and then calls it appropriately. This is called inheritance: HomeHandler inherits behaviour from BaseHandler. (The details are a little more complex than the sketch above, but broadly equivalent.) -- Steven -- http://mail.python.org/mailman/listinfo/python-list
