[Python-Dev] For review: PEP 285: Adding a bool type (original) (raw)

Tim Peters tim.one@comcast.net
Sat, 09 Mar 2002 15:27:10 -0500

[David Abrahams]

...I guess I can see why you're really intending that

>>> 0 or False False but >>> False or 0 0 This sure rubs all my expectations for a bool the wrong way, though.

It has much more to do with expectations for what "and" and "or" do. Note that they're not "operators" in Python, they're control structures, and cannot be overridden. Don't mix bools with ints with control structures, and you won't get surprised; "False or 0" returning 0 in Python is no more surprising than that

if False: x = False else: x = 0

sets x to 0, and oodles of code relies on that equivalence.

I think I'd better just write my own assertion routine, as Guido suggested. I don't like non-obvious language constructs for something so simple (I'd mention ?: here but I don't need the bruises).

Na, do this:

def bool(e): return e and 'True' or 'False'

Then wrap your true/false expressions in bool() calls. All assuming x-version invariance is important to you. When versions of Python before 2.3 become uninteresting, get rid of the bool() function (and so unmask the builtin of the same name).