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    <p>There is quite some indirection here. Follow me carefully.</p> <p>The <code>shelve</code> module is implemented on top of the <a href="http://docs.python.org/2/library/anydbm.html" rel="noreferrer"><code>anydbm</code> module</a>. This module acts as a facade for 4 different specific DBM implementations, and it will pick the first module available when creating a new database, in the following order:</p> <ol> <li><a href="http://docs.python.org/2/library/dbhash.html" rel="noreferrer"><code>dbhash</code></a> (deprecated but still the first <code>anydbm</code> choice). This is a proxy for the <a href="http://docs.python.org/2/library/bsddb.html#module-bsddb" rel="noreferrer"><code>bsddb</code> module</a>, <code>.open()</code> is really <code>bsddb.hashopen()</code></li> <li><a href="http://docs.python.org/2/library/gdbm.html" rel="noreferrer"><code>gdbm</code></a>, Python module for the GNU DBM library, offering more functionality than the <code>dbm</code> module can offer when used with this same lbrary.</li> <li><a href="http://docs.python.org/2/library/dbm.html" rel="noreferrer"><code>dbm</code></a>, a proxy module using either the <code>ndbm</code>, BSD DB and GNU DBM libraries (choosen when Python is compiled).</li> <li><a href="http://docs.python.org/2/library/dumbdbm.html" rel="noreferrer"><code>dumbdbm</code></a>, a pure-python implementation.</li> </ol> <p>It is this range of choices that makes <code>shelve</code> files appear to grow extra extensions on different platforms.</p> <p>The <code>dumbdbm</code> module is the one that adds the <code>.bak</code>, <code>.dat</code> and <code>.dir</code> extensions:</p> <blockquote> <p>Open a dumbdbm database and return a dumbdbm object. The filename argument is the basename of the database file (without any specific extensions). When a dumbdbm database is created, files with <code>.dat</code> and <code>.dir</code> extensions are created.</p> </blockquote> <p>The <code>.dir</code> file is moved to <code>.bak</code> as new index dicts are committed for changes made to the data structures.</p> <p>It means that the <em>other</em> three options for <code>anydbm</code> are not available on your platform.</p> <p>The other formats may give you other extensions. The <code>dbm</code> module may use <code>.dir</code>, <code>.pag</code> or <code>.db</code>, depending on what library was used for that module.</p>
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    1. POWhy does the shelve module in python sometimes create files with different extensions?
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    1. USMartijn Pieters
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    1. COThank you for the answer. just one other thing. Do you know how can I force my program to use dumbdbm not any other modules for databases?
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    2. COCreate two empty files with the `.dir` and `.dat` extensions if they do not yet exist, after which `anydbm` will assume there is already a `dumbdbm` database there and use the `dumbdbm` module.
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