I am using: Python 3.0a2 (r30a2:59382, Dec 17 2007, 08:47:22) [GCC 4.1.2 20070626 (Red Hat 4.1.2-13)] on linux2 IDLE 3.0a1 This seems wrong: >>> while False: print("no") else: print("yes") >>> I expected it to print "yes" because the docs say that the else suite is executed if present and if the loop terminated normally (no break), and this is the case here. This works though: >>> x = False >>> while x: print("no") else: print("yes") yes >>> So it seems that "while False" and "while variable" are giving different behaviour.
python 2.5 has the same behaviour, if you use "while 0:" instead. In compiler.c, there is code that optimizes away blocks like "if 0", "while 0". 'if' correctly emit the else clause, 'while' does not...
This bug is also present in the trunk, with while 0 instead of while False. This appears closely related to issue #1875. In my opinion this is a serious bug in the core language. I'm not sure whether it's serious enough to be considered a showstopper for 2.5.2. In any case, I'm raising the priority to get more eyes on this before 2.5.2.
Here is a patch, made against py3k; it should apply cleanly to the trunk. On the 2.5 branch, compile.c seems identical, but test_grammar.py looks very different; the conversion should be easy. Can someone review and apply it? I don't have svn access at the moment.
