[issue28847] dumbdbm should not commit if in read mode

[Jonathan Ng]

Jonathan Ng added the comment:

#1 makes sense to be backported.

On Thu, Dec 1, 2016 at 8:41 PM, Serhiy Storchaka <report at bugs.python.org>
wrote:

>
> Serhiy Storchaka added the comment:
>
> This example is too artificial.
>
> But there is a real issue: opening read-only files in read mode. Currently
> this causes a PermissionError on closing.
>
> For backward compatibility flags 'r' and 'w' are ignored. I.e. opening
> with 'r' and 'w' creates a file if it is not existing, and opening with 'r'
> allows modifying the database. Since 3.6 this emits deprecation warnings
> (issue21708). In future versions this will be an error.
>
> Proposed patch makes two changes:
>
> 1. The index file no longer written if the database was not modified. This
> increases performance and adds a support of read-only files.
>
> 2. A deprecation warning is raised when the index file is absent in 'r'
> and 'w' modes. In future versions this will be an error.
>
> May be the first change can be backported.
>
> ----------
> keywords: +patch
> stage:  -> patch review
> type: behavior -> enhancement
> versions: +Python 3.7
> Added file: http://bugs.python.org/file45722/dbm_dumb_readonly.patch
>
> _______________________________________
> Python tracker <report at bugs.python.org>
> <http://bugs.python.org/issue28847>
> _______________________________________
>

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