On Sep 4, 3:26 pm, Ruediger <[EMAIL PROTECTED]> wrote: > Hello! > > Executing following little program gives me an TypeError. > > What makes me wonder is that foo does get an argument passed while bar > doesn't. Can anyone explain why?????? > > Thanks > Ruediger > > class foo(list): > __hash__ = lambda x: id(x) > > class bar(list): > __hash__ = id > > _s_ = set() > _s_.add(foo()) > _s_.add(bar()) > > [EMAIL PROTECTED]:~> python test01.py > Traceback (most recent call last): > File "test01.py", line 9, in <module> > _s_.add(bar()) > TypeError: id() takes exactly one argument (0 given)
The answer is fairly technical. For member functions to be bound to instances, they are required to have a __get__ method (which takes instance and owner as parameters). 'id' does not. (Why does 'id' not have a __get__ method?) By contrast, >>> set.add <method 'add' of 'set' objects> >>> dir(_) ['__call__', '__class__', '__delattr__', '__doc__', '__get__', '__getattribute__ ', '__hash__', '__init__', '__name__', '__new__', '__objclass__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__'] 'set.add' does. -- http://mail.python.org/mailman/listinfo/python-list
