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From: Nick Cash <nick.cash@npcinternational.com>
To: "python.list@tim.thechases.com" <python.list@tim.thechases.com>, "python-list@python.org" <python-list@python.org>
Subject: RE: (any)dbm module lacks a context manager
Thread-Topic: (any)dbm module lacks a context manager
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Date: Thu, 31 Jan 2013 19:34:16 +0000
References: <20130131130305.40fc78a8@bigbox.christie.dr>
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Xref: csiph.com comp.lang.python:38010

> >>> import dbm
> >>> with dbm.open("mydb", 'c') as d:
> ...     d["hello"] =3D "world"
> ...
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> AttributeError: '_dbm.dbm' object has no attribute '__exit__'

This error message is somewhat misleading... it actually means you're tryin=
g to use an object as a context manager, and it doesn't implement the conte=
xt manager protocol (defined __enter__ and __exit__ methods). In this case,=
 db.open() returns a dict -like object that is not a context manager. You'd=
 need to refactor your code to something like:

import dbm
d =3D dbm.open("mydb", 'c')
d["hello"] =3D "world"
d.close()=20

You may want to wrap any actions on d with a try-except-finally so you can =
always close the db. If dbm objects were real context managers, they would =
do this for you.=20
This does seem like a useful enhancement. It might be slightly involved to =
do, as the dbm module has multiple implementations depending on what librar=
ies are available on the OS.

-Nick Cash