"Guido van Rossum" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] >I just finished debugging some code that broke after upgrading to > Python 2.4 (from 2.3). Turns out the code was testing list iterators > for their boolean value (to distinguish them from None).
This seem unnecessarily indirect. Why not 'it != None' or now, 'it is not None'? >In 2.3, a > list iterator (like any iterator) is always true. In 2.4, an exhausted > list iterator is false; probably by virtue of having a __len__() > method that returns the number of remaining items. According to 2.4 News, dict iterators also got __len__ method, though I saw no mention of list. > I realize that this was a deliberate feature, I presume there were two reasons: internal efficiency of preallocations (list(some_it) for example) and letting people differentiate iterator with something left to return versus nothing, just as we can differentiate collections with something versus nothing. > and that it exists in > 2.4 as well as in 2.4.1 and will in 2.4.2; yet, I'm not sure I *like* > it. Was this breakage (which is not theoretical!) considered at all? Searching the gmane archive with the link given on the python site for 'iterator len', I could not find any discussion of the __len__ method addition itself. Terry J. Reedy _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
