Bugs item #1328959, was opened at 2005-10-17 15:26 Message generated for change (Comment added) made by rhettinger You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1328959&group_id=5470
Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: None Group: Python 2.4 >Status: Closed >Resolution: Invalid Priority: 5 Submitted By: Christian Höltje (docwhat) Assigned to: Nobody/Anonymous (nobody) Summary: Empty Generator doesn't evaluate as False Initial Comment: The following code doesn't work correctly if the function "generator()" doesn't have any values. if generator(): print "This should only happen when the generator runs yield" print " but it is always true, even if the generator is empty" else: print "this is the expected path when the generator is empty" The workaround is: try: generator().next() print "this is the true case" except StopIteration: print "this is the false case" This means that generators are not transparent and they don't behave as expected (like a list or tuple). I've been bitten by this enough that I am unhappy. :-( ---------------------------------------------------------------------- >Comment By: Raymond Hettinger (rhettinger) Date: 2005-10-17 15:58 Message: Logged In: YES user_id=80475 Your unhappiness is predicated on an invalid set of assumptions. For most generators, it is not possible to know in advance whether the iterator will raise StopIteration on the next call. Also, Guido has pronounced that generators (like most objects) will always evaluate to True. ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1328959&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
