Make shelf instances work with 'with' as context managers

[gruszczy]

BPO	13896
Nosy	@terryjreedy, @ncoghlan, @asvetlov
Files	13896.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/asvetlov'
closed_at = <Date 2012-10-06.10:54:40.786>
created_at = <Date 2012-01-28.11:12:29.545>
labels = ['type-feature']
title = "Make shelf instances work with 'with' as context managers"
updated_at = <Date 2013-01-26.19:20:15.938>
user = 'https://bugs.python.org/gruszczy'

bugs.python.org fields:

activity = <Date 2013-01-26.19:20:15.938>
actor = 'terry.reedy'
assignee = 'asvetlov'
closed = True
closed_date = <Date 2012-10-06.10:54:40.786>
closer = 'asvetlov'
components = []
creation = <Date 2012-01-28.11:12:29.545>
creator = 'gruszczy'
dependencies = []
files = ['24347']
hgrepos = []
issue_num = 13896
keywords = ['patch']
message_count = 10.0
messages = ['152159', '152185', '152236', '152575', '152604', '172122', '172159', '172177', '172178', '180702']
nosy_count = 7.0
nosy_names = ['terry.reedy', 'ncoghlan', 'asvetlov', 'gruszczy', 'python-dev', 'zachary r.', 'Miguel.Angel.Garc\xc3\xada']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue13896'
versions = ['Python 3.4']

[gruszczy]

It would be cool if use could use with to manage shelf object and forget about close.

[zacharyr]

The docs for shelve(see: http://docs.python.org/dev/library/shelve.html#shelve.open) recommend using contextlib.closing for this purpose.

[gruszczy]

Oh, I haven't noticed that. Using contextlib.closing solves my problem. Thanks.

[terryjreedy]

contextlib.closing is an adapter for using objects that have a close method but have not be modernized to be context managers by having _enter__ and __exit__ methods added. Its doc gives the example
with closing(urlopen('http://www.python.org')) as page:
This is now obsolete as the object returned is now a context manager.

A shelf instance would make a better example now, but...
I think it reasonable to update shelve.Shelf also. I believe
def __enter__(self): return self
def __exit__(self, e_typ, e_val, tb): self.close()
are all that are needed. (Nick, true?)

[gruszczy]

closing was solving my problem, but I'll be happy on working on this patch, if you think it's useful after all. I don't think the stage should be test needed, since the patch has tests (I know the drill here ;-)).

[asvetlov]

Filip, please describe why you prevent closing if writeback attribute is not present.
I see comment for __del__ related to bpo-1339007, but at __exit__ call __enter__ has called already and __init__ has finished definitely with success.
Also I would to see reference to http://bugs.python.org/issue1339007 in __del__ comment to cleaner description of issue.

[gruszczy]

Crap, it was so long ago, that I honestly don't remember why I added this if. It made sense back then.

[python-dev]

New changeset 3c1df1ede882 by Andrew Svetlov in branch 'default':
Issue bpo-13896: Make shelf instances work with 'with' as context managers.
http://hg.python.org/cpython/rev/3c1df1ede882

[asvetlov]

Committed. Thanks.
Please fill Python Contributor Agreement: http://www.python.org/psf/contrib/

[terryjreedy]

The patch did not update the doc. See bpo-17040, with proposed patch.