On Mon, 23 Jan 2006 21:43:16 +1100, Steven D'Aprano <[EMAIL PROTECTED]> wrote:
>On Sun, 22 Jan 2006 16:40:48 -0800, Paul Rubin wrote: > >> Steve Holden <[EMAIL PROTECTED]> writes: >>> > The current list function is supposed to be something like a >>> > typecast: >>> > >>> list() isn't a function, it's a type. >> >> I'm not sure what the distinction is supposed to be. "list" is anyway >> callable, and lambda a:list(a) is certainly a function. > > >class Parrot: > def __init__(self): > pass > >Parrot is callable. Is it a function? > No. It is an object that inherits a __call__ method that makes it callable with a (<args>) source syntax trailer in a similar way to an object created with a def (which is a function in python convention, and which also inherits a __call__ method), but the similarity does not make Parrot a function: >>> class Parrot: ... def __init__(self): ... pass ... (BTW you could have inherited a do-nothing __init__ ;-) >>> type(Parrot).mro() [<type 'classobj'>, <type 'object'>] >>> type(Parrot).mro()[0].__call__ <slot wrapper '__call__' of 'classobj' objects> Or, showing more explicitly where it comes from: >>> type(Parrot).mro()[0].__dict__['__call__'] <slot wrapper '__call__' of 'classobj' objects> Invoked: >>> type(Parrot).mro()[0].__dict__['__call__'](Parrot) <__main__.Parrot instance at 0x02EF340C> Hm, actually that is like calling the im_func of the unbound method of a newstyle class ... I think maybe actually Parrot() causes >>> type(Parrot).mro()[0].__dict__['__call__'].__get__(Parrot, type(Parrot))() <__main__.Parrot instance at 0x02EF398C> A function is also an object with a __call__ method. E.g., compare above the line with calling foo (after definition just below) the long way: >>> def foo(): return 'returned by foo' ... >>> type(foo).mro()[0].__dict__['__call__'].__get__(foo, type(foo))() 'returned by foo' Playing with that a little: >>> type(foo).mro() [<type 'function'>, <type 'object'>] >>> type(foo).mro()[0] <type 'function'> >>> type(foo).mro()[0].__call__ <slot wrapper '__call__' of 'function' objects> >>> type(foo).mro()[0].__call__(foo) 'returned by foo' >>> foo.__call__ <method-wrapper object at 0x02EF340C> >>> foo.__call__() 'returned by foo' >>> type(foo).mro()[0].__call__.__get__ <method-wrapper object at 0x02EF340C> >>> type(foo).mro()[0].__call__.__get__(foo, type(foo)) <method-wrapper object at 0x02EF39AC> >>> type(foo).mro()[0].__call__.__get__(foo, type(foo))() 'returned by foo' or >>> foo() 'returned by foo' > >Types are types, classes are classes, functions are functions. classes seem to be classobjs, designed to implement classic class behavior but using the new machinery to achieve compatible integration. > >Admittedly I still confused between the various flavours of functions >(function, bound method, unbound method, class method, static method...) >*wink* but the difference between types and functions is fairly clear. > >Just don't ask about the difference between type and class... *wink* > Why not? ;-) Regards, Bengt Richter -- http://mail.python.org/mailman/listinfo/python-list
