[Python-Dev] bool conversion wart? (original) (raw)

Josiah Carlson jcarlson at uci.edu
Mon Feb 26 19:34:29 CET 2007

Jordan Greenberg <jordangreenberg at gmail.com> wrote:

Guido van Rossum wrote: > How would this change be helpful? I'm utterly mystified by these > suggestions that bool would be more useful if it didn't behave like an > int in arithmetic.

I don't think anyones really saying it would be more useful, it obviously wouldn't, since like Greg said, it wouldn't work in mapping access or set membership like it does now. I think it would be more readable though, since thinks like this: >>> True in set([1]) True or that 5+True is equal to 6 aren't necessarily obvious to someone who doesn't know that True evaluates to 1.

Maybe, but 30-some years of C semantics and another 15 years of Python semantics die hard. a==b for builtin types used to return 1 or 0, now they return True or False. Changing such semantics because some users haven't ever used C or older Pythons would be a bit like changing 'def' to 'fcn' because some users have never used 'def' to define a function. Learn the semantic and move on.

It is elegant to embed bool in int, but to me it screams C. To me, it makes more sense to use an int if you want an int, and to reserve boolean for logic.

You say "screams C" as if it were necessarily a bad thing. Certainly C isn't a perfect language (which is why I use Python), but there are many reasons why I (and others) use (or not) C, but I can just about guarantee you that the semantics of booleans in C help rather than hurt its adoption.

From an elegance/usefulness standpoint, maybe bool should evaluate to 0 and 1. But IMHO, it would eliminate some gotchas and improve readability if it didn't.

You are, of course, entitled to your opinion. From what I understand, there is perhaps one major "gotcha" in the current semantics: bool(str()) isn't correct for anything except for '' and u''. Then again, that isn't a guarantee with str or bool (or list, tuple, dict, deque, set, etc.)

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