Add "mode" parameter to shelve.open

[fomcl]

Feature or enhancement

Proposal:

When using a file-based shelve it is not currently possible to set the file permissions. It is, however, set to default value 666 in the underlying dbm module. It seems like small, non-breaking change to add a mode parameter (default value: 666) parameter to shelve.open

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-113093: add parameter 'mode' in shelve.open #148662

[ammar-Mohamed-elz3eeem]

Can I work on implementing this feature?

[erlend-aasland]

cc. @serhiy-storchaka, who has been working on similar changes to open() methods lately.

[serhiy-storchaka]

It is possible to set the file permissions.

import dbm
import shelve
db = shelve.Shelve(dbm.open(filename, 'c', mode))

[erlend-aasland]

Worth a mention in the docs, Serhiy?

[serhiy-storchaka]

I do not know what can be added that is not in the docs yet.

If you want to use the specific backend (instead the one chosen automatically depending on OS, version, and installed third-party libraries), or pass additional backend arguments, you have no other way as to use the Shelve class directly. It is obvious.

[erlend-aasland]

I ws thinking of adding an example to the shelve docs; currently there is none. OTOH, the docs slightly discourage this practice:

The choice of which database package will be used (such as dbm.ndbm or dbm.gnu) depends on which interface is available. Therefore it is not safe to open the database directly using dbm.

[furkanonder]

@serhiy-storchaka

shelve.open() opens files with 666 permissions via the underlying dbm.open() call. Users cannot control file permissions, which can be problematic in multi-user environments or when storing sensitive data. Other file creation APIs in the stdlib expose mode parameters, but shelve lacks this capability.

The change is straightforward since dbm.open() already accepts a mode parameter:

# Current in DbfilenameShelf.__init__:
Shelf.__init__(self, dbm.open(filename, flag), ...)

# Proposed:
Shelf.__init__(self, dbm.open(filename, flag, mode), ...)

We'd update two function signatures:

• shelve.open() to accept mode=0o666
• DbfilenameShelf.__init__() to pass it through