New submission from Denver Coneybeare <denver.coneybe...@gmail.com>:
dbm.open() with flag="n" raises dbm.error if the given file exists but whichdb
doesn't recognize it. In the documentation for dbm.open() the "n" flag is
documented to "Always create a new, empty database, open for reading and
writing". To me, this implies that if the file exists it will unconditionally
be overwritten with a newly-created database, irrespective of its contents.
The code below illustrates a scenario (and indeed the scenario that I ran into)
where dbm.open(..., flag="n") will throw dbm.error when it should just blow
away the existing file and create a new, empty database:
import dbm
open("test.db", "w").close() # create empty file
dbm.open("test.db", flag="n")
The cause of the exception is that within dbm.open() there is a call to whichdb
to determine the file type. The fix would be to skip this whichdb check if the
"n" flag is specified.
I don't think that this change will cause backward compatibility issues, since
I find it hard to believe that existing applications would rely on this
exception being raised in this scenario. However, to *guarantee* no
compatibility break an alternate fix could leave the current behavior of the
"n" flag and introduce a new flag, perhaps "o" for "overwrite", with this
"unconditional overwrite" behavior.
A proposed patch is attached: dbm_open_n_flag_error_invalid_file_fix_v1.patch
----------
components: Library (Lib)
files: dbm_open_n_flag_error_invalid_file_fix_v1.patch
keywords: patch
messages: 130791
nosy: denversc
priority: normal
severity: normal
status: open
title: dbm.open(..., flag="n") raises dbm.error if file exists and is rejected
by whichdb
type: behavior
versions: Python 3.3
Added file:
http://bugs.python.org/file21108/dbm_open_n_flag_error_invalid_file_fix_v1.patch
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