Boolean tests [was Re: Attack a sacred Python Cow]
steve at REMOVE-THIS-cybersource.com.au
Wed Jul 30 01:59:50 CEST 2008
On Tue, 29 Jul 2008 13:53:07 -0700, Carl Banks wrote:
> Bzzt. "if len(x)!=0" is a simple explicit that would work for this
> class and all built-in containers. (Or should--Steven D'Aprano's
> objections notwithstanding, any reasonable container type should support
> this invariant.
What's the length of an empty list with a sentinel at the end?
What's the length of a binary tree? Does it even have a length?
What's the length of a constant-sized table where each position might be
in use or free?
You're making assumptions about what an empty object "should" look like.
I say, just ask the object if it's empty, don't try to guess how you
would find out. Maybe the object carries around a flag x.isempty. Who
knows? Why do you care? You're basing your code on implementation
details. That should be avoided whenever possible.
> Once again, I'm invoking the contraint against simply using x in a
> boolean context,
So, to put it another way... you want us to give you an example of using
x in a boolean context, but you're excluding any example where we use x
in a boolean context.
Right-o, I've had enough of your trolling. I'm out of here.
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