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

Alex Martelli aleax@aleax.it
Sat, 15 Mar 2003 19:07:35 +0100

On Saturday 15 March 2003 04:59 pm, Christian Tismer wrote: ...

Complex just has no total order, which makes it impossible to provide a meaningful default ordering.

Back in Python 1.5.2 times, the "impossible to provide" ordering was there. No more (and no less!) "meaningful" than, say, comparisons between (e.g.) lists, numbers, strings and dicts, which are still provided as of Python 2.3.

I agree that my statement does not apply when putting non-sortable things into a list. But I don't believe

A list containing ONE complex number and (e.g.) three strings is sortable. So, there are NO "non-sortable things".

A list is non-sortable (unless by providing a custom compare, as you pointed out) if it contains a complex number and any other number -- so, there are "non-sortable LISTS" (unless suitable custom compares are used), but still no "non-sortable THINGS" in current Python.

that people are putting widely different types into a list in order to sort them. (Although there is an arbitrary order between strings and numbers, which I would drop in Python 2.4, too).

Such a change would indeed enormously increase the number of non-sortable (except by providing custom compares) lists. So, for example, all places which get and sort the list of keys in a dictionary in order to return or display the keys should presumably do the sorting within a try/except? Or do you think a dictionary should also be constrained to have keys that are all comparable with each other (i.e., presumably, never both string AND number keys) as well as hashable?

I fail to see how forbidding me to sort the list of keys of any arbitrary dict will enhance my productivity in any way -- it's bad enough (in theory -- in practice it doesn't bite much as complex numbers are used so rarely) with the complex numbers thingy, why make it even worse by inventing a novel "strings vs numbers" split?

Since when is Python about forbidding the user to do quite normal things such as sorting the list of keys of any arbitrary dictionary for more elegant display -- for no practically useful purpose that I've ever seen offered, in brisk violation of "practicality beats purity"?

Alex