fix code example in docs for built-in reduce()

[cjerdonek]

BPO	16077
Nosy	@cjerdonek, @serhiy-storchaka

^{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/cjerdonek'
closed_at = <Date 2012-09-29.18:54:04.817>
created_at = <Date 2012-09-28.08:55:51.868>
labels = ['easy', 'type-feature', 'docs']
title = 'fix code example in docs for built-in reduce()'
updated_at = <Date 2012-09-29.19:07:42.215>
user = 'https://github.com/cjerdonek'

bugs.python.org fields:

activity = <Date 2012-09-29.19:07:42.215>
actor = 'serhiy.storchaka'
assignee = 'chris.jerdonek'
closed = True
closed_date = <Date 2012-09-29.18:54:04.817>
closer = 'chris.jerdonek'
components = ['Documentation']
creation = <Date 2012-09-28.08:55:51.868>
creator = 'chris.jerdonek'
dependencies = []
files = []
hgrepos = []
issue_num = 16077
keywords = ['easy']
message_count = 5.0
messages = ['171419', '171425', '171586', '171587', '171591']
nosy_count = 4.0
nosy_names = ['chris.jerdonek', 'docs@python', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue16077'
versions = ['Python 2.7']

[cjerdonek]

Date: Thu, 6 Sep 2012 20:38:21 +0800
To: docs@python.org
Subject: [docs] There is bug about the built-in function reduce in the
document

I found a bug in the document about reduce :
http://docs.python.org/library/functions.html#reduce

Here is the patch:
def reduce(function, iterable, initializer=None):
it = iter(iterable)
if initializer is None:
try:
initializer = next(it)
except StopIteration:
raise TypeError('reduce() of empty sequence with no initial
value')
accum_value = initializer

• for x in iterable:

• for x in it:
  accum_value = function(accum_value, x)
  return accum_value

It duplicated the first element of iterable

For example:
In [4]: reduce(lambda x,y:x+y, [1,2,3,4])
Out[4]: 10

In [5]: docreduce.reduce(lambda x,y:x+y ,[1,2,3,4])
Out[5]: 11

(from: http://mail.python.org/pipermail/docs/2012-September/010513.html and
http://mail.python.org/pipermail/docs/2012-September/010526.html )

[serhiy-storchaka]

Indeed.

Will probably want to add an example with 1-element sequence for functools.reduce in Doc/howto/functional.rst.

[python-dev]

New changeset a6779524962c by Chris Jerdonek in branch '2.7':
Close issue bpo-16077: fix code example in documentation of reduce() built-in (from docs@).
http://hg.python.org/cpython/rev/a6779524962c

[cjerdonek]

Serhiy, feel free to create a new issue for Doc/howto/functional.rst if you feel an addition there is warranted.

[serhiy-storchaka]

I thought and decided it wasn't worth it. Howtos for general cases, and not for corner cases.