Documentation of itertools.accumulate is confused

[MLModel]

BPO	20103
Nosy	@akuchling, @rhettinger, @terryjreedy, @ezio-melotti, @MLModel
Files	accumulate_doc.patch accumulate2.diff: Second (final) revision of the doc patch for accumulate.

^{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/akuchling'
closed_at = <Date 2014-04-16.02:30:21.755>
created_at = <Date 2014-01-01.16:12:00.835>
labels = ['easy', 'type-feature', 'docs']
title = 'Documentation of itertools.accumulate is confused'
updated_at = <Date 2014-04-16.02:30:21.742>
user = 'https://github.com/MLModel'

bugs.python.org fields:

activity = <Date 2014-04-16.02:30:21.742>
actor = 'akuchling'
assignee = 'akuchling'
closed = True
closed_date = <Date 2014-04-16.02:30:21.755>
closer = 'akuchling'
components = ['Documentation']
creation = <Date 2014-01-01.16:12:00.835>
creator = 'MLModel'
dependencies = []
files = ['34839', '34878']
hgrepos = []
issue_num = 20103
keywords = ['patch', 'easy']
message_count = 6.0
messages = ['207135', '207260', '216172', '216321', '216419', '216420']
nosy_count = 8.0
nosy_names = ['akuchling', 'rhettinger', 'terry.reedy', 'chrish42', 'ezio.melotti', 'MLModel', 'docs@python', 'python-dev']
pr_nums = []
priority = 'low'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue20103'
versions = ['Python 3.3', 'Python 3.4']

[MLModel]

The documentation of itertools.accumulate (10.1) starts out with 2 misleading sentences: "Make an iterator that returns accumulated sums. Elements may be any addable type..." It then goes on to show examples of using the func parameter added in 3.3 that are not additions. It should be changed to something like: "Make an iterator that returns accumulated values. Elements may be any type that can be an argument to func. Func defaults to addition, so by default elements can be any addable types, ..." My wording is awkward, but you get the idea. I think this is a significant documentation issue, not just a nit.

[terryjreedy]

Somewhat orthogonal to Mitchell's suggestion, I would change 'returns' to 'yields' and expand 'elements' to 'elements of *iterable*'.

[chrish42]

The following patch improves (I hope) the documentation of itertools.accumulate. Comments and feedback welcome.

Terry, I did not implement your suggestion of changing "returns" to "yields", as it would have made things inconsistent with the documentation (and docstrings) of pretty much all the other generators in the itertools module, as they all use this idiom also. If one of the Python documentation experts thinks this change is also a good idea, please just open a new bug report for that and put me in the nosy list, and I'll do the change for all relevant generators in the itertools module.

[chrish42]

Second revision, incorporating comments. Also document the behavior when passed an empty input iterable.

[python-dev]

New changeset 9e1d2150fff2 by Andrew Kuchling in branch 'default':
bpo-20103: Rewrite description of itertools.accumulate().
http://hg.python.org/cpython/rev/9e1d2150fff2

[akuchling]

Thanks for your patch!