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

[E. Madison Bray]

On Thu, Nov 29, 2018 at 12:16 PM Chris Angelico <rosuav at gmail.com> wrote:
>
> 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.

Rebind where?  How?  In sage.__init__?  How do you think that will fly
with other packages loaded in the same interpreter?