fix map() statement in list comprehension example

[cjerdonek]

BPO	16073
Nosy	@cjerdonek
Files	issue16073.patch

^{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 2012-09-28.14:30:14.454>
created_at = <Date 2012-09-28.03:50:23.772>
labels = ['easy', 'type-feature', 'docs']
title = 'fix map() statement in list comprehension example'
updated_at = <Date 2012-09-28.14:30:14.453>
user = 'https://github.com/cjerdonek'

bugs.python.org fields:

activity = <Date 2012-09-28.14:30:14.453>
actor = 'chris.jerdonek'
assignee = 'chris.jerdonek'
closed = True
closed_date = <Date 2012-09-28.14:30:14.454>
closer = 'chris.jerdonek'
components = ['Documentation']
creation = <Date 2012-09-28.03:50:23.772>
creator = 'chris.jerdonek'
dependencies = []
files = ['27332']
hgrepos = []
issue_num = 16073
keywords = ['patch', 'easy']
message_count = 5.0
messages = ['171405', '171459', '171468', '171474', '171476']
nosy_count = 4.0
nosy_names = ['chris.jerdonek', 'docs@python', 'python-dev', 'inglesp']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue16073'
versions = ['Python 3.2', 'Python 3.3']

[cjerdonek]

Date: Thu, 20 Sep 2012 15:14:36 -0400
To: docs@python.org
Subject: [docs] map objects are not lists

5.1.3. List Comprehensions<http://docs.python.org/dev/tutorial/datastructures.html#list-comprehensions\>

List comprehensions provide a concise way to create lists. Common
applications are to make new lists where each element is the result of some
operations applied to each member of another sequence or iterable, or to
create a subsequence of those elements that satisfy a certain condition.

For example, assume we want to create a list of squares, like:
>>>

>>> squares = []>>> for x in range(10):... squares.append(x**2)...>>> squares[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

We can obtain the same result with:

squares = [x**2 for x in range(10)]

This is also equivalent to squares = map(lambda x: x**2, range(10)), but
it?s more concise and readable.

I think that the last sentence above should read:

squares = list(map(lambda x: x**2, range(10)))

In other words, the map function returns a map object, not a list object,
so the list() function needs to be used to convert it to something that is
truly equivalent to the previous definitions of "squares". (In case it
matters, I am using Python-3.3.0rc2 on RHEL 6.3.)

(from http://mail.python.org/pipermail/docs/2012-September/010525.html )

[inglesp]

Have attached a patch with suggested update.

Have also grepped for similar issues elsewhere in documentation, and haven't found anything, but may have missed something.

[cjerdonek]

2.7 is not affected.

[python-dev]

New changeset 6c96878eb729 by Chris Jerdonek in branch '3.2':
Close issue bpo-16073: fix map() example in list comprehension documentation.
http://hg.python.org/cpython/rev/6c96878eb729

New changeset 8a4a88b1e964 by Chris Jerdonek in branch 'default':
Close issue bpo-16073: merge fix from 3.2.
http://hg.python.org/cpython/rev/8a4a88b1e964

[cjerdonek]

Thanks for helping with the patch and search, Peter.