[Python-Dev] Re: Re: lists v. tuples (original) (raw)

Andrew Koenig ark@research.att.com
16 Apr 2003 11:20:52 -0400

So the first time you care is the first time f(x, y) returns nonzero. Now you can find out what kind of function f is by calling f(y, x). If f(y, x) returns zero, f is <. Otherwise, it's a 3-way comparison.

Guido> Right. There's no flaw in this logic, but I'd hate to have to Guido> explain it over and over... I don't want people to believe Guido> that Python can somehow magically sniff the difference between Guido> two functions; they might expect it in other contexts.

I can understand your reluctance -- I was just pointing out that it's possible.

However, I'm slightly dubious about the x.sort(lt=f) vs x.sort(cmp=f) technique because it doesn't generalize terribly well.

If I want to write a function that takes a comparison function as an argument, and eventualy passes that function to sort, what do I do? Something like this?

    def myfun(foo, bar, lt=None, cmp=None):
            # ...
            x.sort(lt=lt, cmp=cmp)
            # ...

and assume that sort will use None as its defaults also? Or must I write

            if lt==None:
                    x.sort(cmp=cmp)
            else:
                    x.sort(lt=lt)

Either way it's inconvenient.

So I wonder if it might be better, as a way of allowing sort to take two different types of comparison functions, to distinguish between them by making them different types.

-- Andrew Koenig, ark@research.att.com, http://www.research.att.com/info/ark