Make mmap.write return the number of bytes written like other write methods

[jstasiak]

BPO	26335
Nosy	@Yhg1s, @berkerpeksag, @vadmium, @jstasiak
Files	mmap_write_return_count.patch mmap_write_return_count2.patch mmap_write_return_count3.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 = None
closed_at = <Date 2016-03-02.17:31:09.579>
created_at = <Date 2016-02-10.22:55:37.908>
labels = ['extension-modules', 'type-feature']
title = 'Make mmap.write return the number of bytes written like other write methods'
updated_at = <Date 2016-03-03.00:02:26.588>
user = 'https://github.com/jstasiak'

bugs.python.org fields:

activity = <Date 2016-03-03.00:02:26.588>
actor = 'jstasiak'
assignee = 'none'
closed = True
closed_date = <Date 2016-03-02.17:31:09.579>
closer = 'berker.peksag'
components = ['Extension Modules']
creation = <Date 2016-02-10.22:55:37.908>
creator = 'jstasiak'
dependencies = []
files = ['41890', '42014', '42026']
hgrepos = []
issue_num = 26335
keywords = ['patch']
message_count = 8.0
messages = ['260053', '260706', '260750', '260759', '260847', '261128', '261129', '261143']
nosy_count = 5.0
nosy_names = ['twouters', 'python-dev', 'berker.peksag', 'martin.panter', 'jstasiak']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue26335'
versions = ['Python 3.6']

[jstasiak]

Since mmap objects are said to "behave like both bytearray and like file objects" I believe it's appropriate for the mmap.write() method to return the number of bytes written like write() of other file objects/interfaces I could find in the standard library for consistency reasons:

https://docs.python.org/3/library/io.html#io.BufferedIOBase.write
https://docs.python.org/3/library/io.html#io.BufferedWriter.write
https://docs.python.org/3/library/io.html#io.RawIOBase.write
https://docs.python.org/3/library/io.html#io.TextIOBase.write

Why I believe this would be useful: code that writes to file objects and tests the number of bytes/characters written right now will likely fail when it's passed a mmap object because its write() method returns None. With this patch applied it'll work transparently.

Please find proposed patch attached, I included information about the exception type in the documentation as it seems fitting (apologies for generating the patch using Git, I'll generate using Mercurial if necessary).

[berkerpeksag]

Thanks for the patch, Jakub. I don't use mmap module much so I don't have an opinion about the feature, but it sounds reasonable.

I left some review comments on Rietveld: http://bugs.python.org/review/26335/

[jstasiak]

Oops, sorry for the silliness in the C code, thanks for reviewing. I modified as suggested, please find the new patch attached.

[vadmium]

Patch looks okay to me. I guess it would be good to write a What’s New entry as well.

[jstasiak]

Thank you. I didn't know whether to add an entry to Doc/whatsnew/3.6.rst, Misc/NEWS or both so I chose both, feel free to modify/remove as needed.

The new patch also doesn't have a typo in the versionchanged directive present in the version 2. I noticed more typos like this (single colon instead of double colon), I'll create a separate issue.

[python-dev]

New changeset ba71aecec943 by Berker Peksag in branch 'default':
Issue bpo-26335: Make mmap.write() return the number of bytes written like
https://hg.python.org/cpython/rev/ba71aecec943

[berkerpeksag]

Thanks for the patch, Jakub!

[jstasiak]

Glad I could help, thanks for merging!