On Mon, Dec 5, 2011 at 9:04 AM, Roy Smith <r...@panix.com> wrote: > Consider the following django snippet. Song(id) raises DoesNotExist if > the id is unknown. > > try: > songs = [Song(id) for id in song_ids] > except Song.DoesNotExist: > print "unknown song id (%d)" % id > > Is id guaranteed to be in scope in the print statement? I found one > thread ( > http://mail.python.org/pipermail/python-bugs-list/2006-April/033235.html) > which says yes, but hints that it might not always be in the future. Now > that we're in the future, is that still true? And for Python 3 also? >
In Python2, id will always be in scope, unless the first iteration fails (aka, an empty iterable, or a custom iterable which raises an exception before yielding a result). I believe in Python3, the scoping of list comprehensions was changed to match that of generator expressions, which is that the loop variable(s) fall out of scope outside of the expression. > > The current docs, > http://docs.python.org/tutorial/datastructures.html#list-comprehensions, > are mute on this point. > -- > http://mail.python.org/mailman/listinfo/python-list >
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