On May 16, 4:17 pm, Christian Heimes <li...@cheimes.de> wrote: > > First, I've looked a fair bit and can't find how one can find the base > > classes of a subclass? isinstance and issubclass sort of do the > > opposite of what I want. Surely somewhere there is something like > > > MyThingee.something.orOther.baseClasses() > > You can get the direct parents of a class with the attribute __bases__. > The class attribute __mro__ returns a tuple of for the method resolution > order. But instead of poking around yourself I suggest you use the > inspect module. It provides a high level interface. > > >>> class Example: > > ... pass > ...>>> Example.__bases__ > (<class 'object'>,) > >>> Example.__mro__ > > (<class '__main__.Example'>, <class 'object'>) > > > But what happens if I try to subclass function? > > > First attempt: > > >>>> class MyFunction(function): > > .... pass > > .... > > Traceback (most recent call last): > > File "<stdin>", line 1, in<module> > > NameError: name 'function' is not defined > > There is no object called function in the list of builtins. You can't > subclass from function anyway so there is no point in accessing the > function object. If you want to create some callable class you have to > provide a method call "__call__". It's called when you call the > instances of your class like a function. > > >>> def a(): > > ... pass > ...>>> type(a) > <class 'function'> > >>> function = type(a) > >>> class MyFunc(function): > > ... pass > ... > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: type 'function' is not an acceptable base type > > > Anyway, again can you point me to somewhere that I can learn more? In > > particular, is there a list somewhere of the builtin types that are > > not subclassable? > > I don't think it's documented anyway. You have to try yourself. In > general you don't have to subclass builtin types. Some classes are > tricky to subclass like e.g. immutable classes (str, bytes) or dict.
It's not a list, but you can tell if a given type is subclassable by testing bit 10 of the __flags__ attribute: type(lambda:0).__flags__ & 1024 -> 0 int.__flags__ & 1024 -> 1024 The reason some types are not subclassable is simply because there's more involved to write a type at the C level that's subclassable. For a lot of types the work wasn't considered worth it. If you think you want to subclass function, consider whether you can do what you want with decorator syntax. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
