[Python-ideas] __len__() for map()

[Chris Angelico]

On Thu, Nov 29, 2018 at 10:14 PM E. Madison Bray <erik.m.bray at gmail.com> wrote:
> P.S.
>
> > > This is necessary because if I have a function that used to take, say,
> > > a list as an argument, and it receives a `map` object, I now have to
> > > be able to deal with map()s,
> >
> > If a function is documented as requiring a list, or a sequence, or a
> > length object, it is a user bug to pass an iterator.  The only thing
> > special about map and filter as errors is the rebinding of the names
> > between Py2 and Py3, so that the same code may be good in 2.x and bad in
> > 3.x.
>
> It's not a user bug if you're porting a massive computer algebra
> application that happens to use Python as its implementation language
> (rather than inventing one from scratch) and your users don't need or
> want to know too much about Python 2 vs Python 3.  Besides, the fact
> that they are passing an iterator now is probably in many cases a good
> thing for them, but it takes away my ability as a developer to find
> out more about what they're trying to do, as opposed to say just being
> given a list of finite size.

If that's the case, then it should be no problem to rebind
builtins.map to return a list. Problem solved.

ChrisA