On Thu, Jul 10, 2008 at 6:28 AM, Antoine Pitrou <[EMAIL PROTECTED]> wrote: > Carl Johnson <carl <at> carlsensei.com> writes: >> >> However, it can be argued that in Python 3 list comprehensions should be >> thought of as "syntatic sugar" for ``list(generator expression)`` not a >> for-loop with an accumulator. (This seems to be the motivation for no >> longer "leaking" variables from list comprehensions into their enclosing >> namespace.) > > I don't know the exact history but I think leaking the iteration variable > didn't have any practical use and could be the possible cause of subtle bugs, > which is a sufficient reason for changing that behaviour. Consistency is an > added bonus :-) > >> This raises the question, do we need both a ``break`` statement and >> ``raise StopIteration``? Can the former just be made into syntatic sugar >> for the later? Or is this the hobgoblin of a little mind? > > I'd say the latter :-) > > Also, I don't see where consistency is improved. IMO, StopIteration is meant > to > be raised by the code which produces the iterator, not by the code consuming > it > - and even less by third-party, non-iterator related code. Otherwise it's an > application bug. > > That is, in your example: > > >>> def f(x): > ... if x > 5: raise StopIteration > ... > >>> list(x for x in range(100) if not f(x)) > [0, 1, 2, 3, 4, 5] > > f() certainly shouldn't raise a StopIteration. There's no reason for doing > that, other than taking dirty implementation shortcuts and ending up with > difficult to maintain code. > > (if you want to stop an iterator based on some predicate you can use > itertools.takewhile())
To be sure, IMO the generator expression is wrong in interpreting the StopIteration exception! It should fail the same way the list comprehension fails. -- --Guido van Rossum (home page: http://www.python.org/~guido/) _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
