Add an intersperse function to itertools

[javawizard]

BPO	21414
Nosy	@rhettinger, @merwok

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/rhettinger'
closed_at = <Date 2014-05-04.02:13:34.387>
created_at = <Date 2014-05-02.07:39:41.789>
labels = ['type-feature']
title = 'Add an intersperse function to itertools'
updated_at = <Date 2014-05-04.02:13:34.385>
user = 'https://bugs.python.org/javawizard'

bugs.python.org fields:

activity = <Date 2014-05-04.02:13:34.385>
actor = 'rhettinger'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2014-05-04.02:13:34.387>
closer = 'rhettinger'
components = []
creation = <Date 2014-05-02.07:39:41.789>
creator = 'javawizard'
dependencies = []
files = []
hgrepos = []
issue_num = 21414
keywords = []
message_count = 4.0
messages = ['217746', '217764', '217814', '217854']
nosy_count = 4.0
nosy_names = ['rhettinger', 'eric.araujo', 'cvrebert', 'javawizard']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = None
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue21414'
versions = ['Python 3.5']

[javawizard]

Itertools would benefit greatly from a function (which I've named intersperse, after Haskell's equivalent) for yielding the items of an iterator with a given value placed between each. Sort of a str.join-like function, but for arbitrary sequences.

Something like:

>>> list(itertools.intersperse(1, [2, 3, 4]))
[2, 1, 3, 1, 4]

[merwok]

I looked for a previous discussion of this on the Python mailing lists and found nothing.

Existing solutions include https://twitter.com/snim2/status/393821419114483712 and http://stackoverflow.com/questions/5655708/python-most-elegant-way-to-intersperse-a-list-with-an-element

Raymond is the one to decide whether this should be added. If he doesn't comment in the near future, feel free to propose this on python-ideas to see if people like it. You may also want to ask maintainers of projects like more-itertools if they have a similar function and if people use it.

[rhettinger]

What is the use case for interspersing values? I've not run across anything like it ever before.

[rhettinger]

I've looked into this a bit more. Even in Haskell, it seems that use case is for str.join() which we already have. I don't see intersperse() in any other functional languages. That suggests that its use cases aren't sufficiently common to warrant adding it to the standard library.

Thank you for the submission.