On 06/15/2013 09:30 PM, Jim Mooney wrote:
##This is puzzling me. If I check the equality of 0, None, empty string, and empty list with False, ##only zero satisfies the equality. But if I use them in a not statement, they all turn out False. ##What gives?#Using C:\Python33\python.exe on Win 7 in c:\python33\jimprogs print('Zero is equal to False' if 0 == False else 'Zero is NOT equal to False') print('None is equal to false' if None == False else 'None is NOT equal to false') print('Empty string is equal to False' if '' == False else 'Empty string is NOT equal to False') print('Empty list is equal to false' if [] == False else 'Empty list is NOT equal to false') print() print('Zero is equal to False' if not 0 else 'Zero is NOT equal to False') print('None is equal to false' if not None else 'None is NOT equal to false') print('Empty string is equal to False' if not '' else 'Empty string is NOT equal to False') print('Empty list is equal to False' if not [] else 'Empty list is NOT equal to false') ##Results: ## ##Zero is equal to False ##None is NOT equal to false ##Empty string is NOT equal to False ##Empty list is NOT equal to false ## ##Zero is equal to False ##None is equal to false ##Empty string is equal to False ##Empty list is equal to False
Why such a convoluted way of expressing yourself? Especially the second half when the statements are clearly different than what you're testing.
False is equivalent to the int 0 for historical reasons, back before there was a separate boolean type. Likewise True is equivalent to the int 1. You shouldn't write any code that counts on it, however.
You don't say which of the remaining ones in the first group are surprising. False is not the same as any other type except the special one I already mentioned.
As for the second group, applying the not operator will produce exactly True or False, the same way that applying bool() will. The only difference is that if one would produce True, the other will produce False. That's what 'not' means. But it's certainly not doing a value comparison like your literal claims. If the item is truthy, not produces False. And if the item is falsey, not produces True.
-- DaveA _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
