[Python-ideas] Add 'interleave' function to itertools?

[Oscar Benjamin]

On 8 August 2013 19:48, Tim Peters <tim.peters at gmail.com> wrote:
>
> To the non-expert, which itertools-like functionalities are "core" -
> which should be derived from which others - is a mystery.  So I'm with
> David on throwing them all in, "at least those that have intuitive and
> obvious names".  Let a thousand redundancies bloom ;-)

They should at least go in a different module. Currently each of those
recipes is already available in more-itertools (including the proposed
first()):
http://pythonhosted.org/more-itertools/api.html

Also if they're going to become anything more than recipes then they
need to be looked at more carefully. I don't really think many of
these belong in the stdlib.

For example why not just use generators? I would find generators
easier to understand than some of these recipes e.g.:

   sum(1 for x in data if x > threshold)

or

   sum(x > threshold for x in data)

are easier to understand than

   quantify(data, lambda x: x > threshold)

even if you're using a named function.

I think that consume() should be included in itertools. flatten() is a
synonym for chain.from_iterable and there has been some discussion
that this could go into builtins (the disagreement only seemed to be
about the name). I want take() to have different semantics than it
does i.e.:

    def take(iterable, n):
        chunk = list(islice(iterable, n))
        if len(chunk) != n:
            raise ValueError('%n items requested but %n found' % (n,
len(chunk)))
        return chunk

Similarly grouper() probably doesn't do what anyone really wants
(since it discards the end of the iterable). It should really be:

    def grouper(iterable, chunksize):
        islices = map(islice, repeat(iter(iterable)), repeat(chunksize))
        return takewhile(bool, map(list, islices))

Some recipes are just unnecessary such as random_product() which is
really just a long way to write something like:

    random_pair = (random.choice(s1), random.choice(s2))

Same goes for random_permutation, random_combination, and
random_combination_with_replacement: if you're just going to build a
collection out of each iterable then what does this have to do with
iterators?

The partition() recipe is only useful if you can think of a clever way
of using it. How would you use it to do anything that would be better
than just building a list (since that's what tee() will do internally
if you consume either of the iterators)?

I use itertools all the time but really the only recipes I would use
in my own code are consume() (with the second argument made optional),
pairwise() and powerset().


Oscar