integer >= 1 == True and integer.0 == False is bad, bad, bad!!!

[Steven D'Aprano]

On Mon, 12 Jul 2010 19:28:28 -0600, Ian Kelly wrote:

> On Mon, Jul 12, 2010 at 6:18 PM, Steven D'Aprano
> <steve at remove-this-cybersource.com.au> wrote:
>>> I prefere to explicitly write what I want to test:
>>>
>>> if myInt <> 0:
>>
>> I would argue against that. Why do you, the coder, care about the
>> specific details of treating ints in a boolean context? The int type
>> itself knows, leave the decision to it.
> 
> I think you're missing the point.  He's not using ints in a boolean
> context.  If it were a boolean context, he would be using bools in the
> first place.

Of course he is -- he's branching on an int (a boolean context), and 
explicitly writing out the test as myInt <> 0. In fact, that test could 
just as easily be written as bool(myInt), which has the benefit of being 
even more explicit that you want a bool.

It's also silly. Explicitness is not always a virtue. Beginners sometimes 
write things like:

s = "hello "
t = "world"
print str(s + t)

and we rightly shake our heads at the sheer n00b-ness of it. Writing the 
explicit tests:

if bool(myInt):

or even:

if myInt <> 0:

are firmly in the same category. The only difference is that it is more 
familiar and therefore comfortable to those who are used to languages 
that don't have Python's truth-testing rules.



> What he is objecting to is the practice of testing for
> special cases of ints (i.e. 0) by treating them as bools.  The specific
> details of converting ints to bools are very much relevant here; as long
> as 0 is false, it works.  If -1 is false (a semantic I have actually
> seen used), then it does not.

You've seen -1 being used as false? Where? Are you still talking about 
Python builtins or language semantics?

If you're about to say string.find(substring), no, absolutely not. find 
does not return a true/false flag, it returns an index, with -1 the 
sentinel for Not Found. This is not a flag!

In fact, one of the motivations for adding bools to Python was to avoid 
people mistakenly thinking that cmp(a, b) returned a flag 0, 1 when it 
actually returns a three-state -1, 0, 1. This was a common source of 
errors before Python got bools.


-- 
Steven