[Python-ideas] Fwd: unpacking generalisations for list comprehension

[אלעזר]

On Thu, Oct 13, 2016 at 5:10 PM Steven D'Aprano <steve at pearwood.info> wrote:

> On Thu, Oct 13, 2016 at 10:37:35AM +0200, Sven R. Kunze wrote:
> > About the list constructor: we construct a list by writing [a,b,c] or by
> > writing [b for b in bs]. The end result is a list
>
> I construct lists using all sorts of ways:
>

I think there is a terminology problem here (again). "Constructor" in OOP
has a specific meaning, and "constructor" in functional terminology has a
slightly different meaning. I guess Sven uses the latter terminology
because pattern matching is the dual of the constructor - it is a
"destructor" - and it feels appropriate, although admittedly confusing. In
this terminology, map(), zip() etc. are definitely not constructors. there
is only one "constructor" (list()), and there are functions that may use it
as their implementation detail. In a way, [1, 2, 3] is just a syntactic
shorthand for list construction, so it is reasonable to a call it a
constructor.

This terminology is not a perfect fit into the object-oriented world of
Python, but it is very helpful in discussion of patterns how to apply them
uniformly, since they were pretty much invented in the functional world
(ML, I think, and mathematics). One only needs to be aware of the two
different meaning, and qualify if needed, so that we won't get lost in
terminology arguments again.

Elazar
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