Am 07.03.2013 17:00, schrieb Ian Kelly: > On Thu, Mar 7, 2013 at 4:22 AM, Wolfgang Maier > <wolfgang.ma...@biologie.uni-freiburg.de> wrote: >> Well, it skips the costly len() call because your iter(Foo()) returns >> iter(range()) under the hood and list() uses that object's __len__() method. > > Iterators do not generally have __len__ methods. > >>>> len(iter(range(10))) > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: object of type 'range_iterator' has no len()
But iterators have a length hint method that are used for some optimizations and preallocations, too. >>> i = iter(range(10)) >>> i.__length_hint__() 10 See http://www.python.org/dev/peps/pep-0424/ Christian -- http://mail.python.org/mailman/listinfo/python-list
