Incorrect use of c_char_p in example code

[rrt]

BPO	37571
Nosy	@amauryfa, @abalkin, @meadori, @zooba, @miss-islington, @tirkarthi
PRs	bpo-37571: Add 'b' to prevent the TypeError exception. #14721 [3.8] bpo-37571: Add 'b' to prevent the TypeError exception. (GH-14721) #14762 [3.7] bpo-37571: Add 'b' to prevent the TypeError exception. (GH-14721) #14763 bpo-37571: Remove extra space in ctypes docs #14764 [3.8] bpo-37571: Remove extra space in ctypes docs (GH-14764) #14766 [3.7] bpo-37571: Remove extra space in ctypes docs (GH-14764) #14767

^{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 = None
closed_at = <Date 2019-07-14.08:14:38.349>
created_at = <Date 2019-07-12.07:40:49.474>
labels = ['ctypes', '3.7', '3.8', '3.9', 'docs']
title = 'Incorrect use of c_char_p in example code'
updated_at = <Date 2019-07-14.08:24:38.449>
user = 'https://bugs.python.org/rrt'

bugs.python.org fields:

activity = <Date 2019-07-14.08:24:38.449>
actor = 'miss-islington'
assignee = 'docs@python'
closed = True
closed_date = <Date 2019-07-14.08:14:38.349>
closer = 'steve.dower'
components = ['Documentation', 'ctypes']
creation = <Date 2019-07-12.07:40:49.474>
creator = 'rrt'
dependencies = []
files = []
hgrepos = []
issue_num = 37571
keywords = ['patch']
message_count = 9.0
messages = ['347725', '347727', '347873', '347875', '347876', '347878', '347879', '347882', '347884']
nosy_count = 8.0
nosy_names = ['amaury.forgeotdarc', 'belopolsky', 'meador.inge', 'docs@python', 'steve.dower', 'rrt', 'miss-islington', 'xtreak']
pr_nums = ['14721', '14762', '14763', '14764', '14766', '14767']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue37571'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[rrt]

The CTypes documentation has this example:

>>> s = c_char_p()
>>> s.value = "abc def ghi"
>>> s.value
'abc def ghi'
>>> s.value is s.value
False
>>>

It appears not to have been updated since Python 2: in Python 3, you can't assign a str to a c_char_p. If one tries the example code above, one gets:

>>> s = c_char_p()
>>> s.value = "abc def ghi"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: bytes or integer address expected instead of str instance

Using a bytes works:

>>> s = c_char_p()
>>> s.value = b"abc def ghi"
>>> s.value
b'abc def ghi'
>>> s.value is s.value
False
>>>

Hence adding the two "b"s is an obvious fix.

Note that the similar example with c_wchar_p does work fine with str.

[tirkarthi]

Thanks for the report. Looks like a valid issue to me. Would you like to create a PR?

[zooba]

New changeset 6b92958 by Steve Dower (Michele Angrisano) in branch 'master':
bpo-37571: Add 'b' to prevent the TypeError exception. (GH-14721)
6b92958

[miss-islington]

New changeset e7c114d by Miss Islington (bot) in branch '3.8':
bpo-37571: Add 'b' to prevent the TypeError exception. (GH-14721)
e7c114d

[miss-islington]

New changeset d7caf75 by Miss Islington (bot) in branch '3.7':
bpo-37571: Add 'b' to prevent the TypeError exception. (GH-14721)
d7caf75

[zooba]

New changeset 68c74d0 by Steve Dower in branch 'master':
bpo-37571: Remove extra space in ctypes docs (GH14764)
68c74d0

[zooba]

Thanks for the patch!

[miss-islington]

New changeset 4f733f4 by Miss Islington (bot) in branch '3.8':
bpo-37571: Remove extra space in ctypes docs (GH14764)
4f733f4

[miss-islington]

New changeset 13c89f3 by Miss Islington (bot) in branch '3.7':
bpo-37571: Remove extra space in ctypes docs (GH14764)
13c89f3