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POVersion number comparison in Python
 

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    <p>I want to write a <code>cmp</code>-like function which compares two version numbers and returns <code>-1</code>, <code>0</code>, or <code>1</code> based on their compared valuses.</p> <ul> <li>Return <code>-1</code> if version A is older than version B</li> <li>Return <code>0</code> if version A and B are equivalent</li> <li>Return <code>1</code> if version A is newer than version B</li> </ul> <p>Each subsection is supposed to be interpreted as a number, therefore 1.10 > 1.1. </p> <p>Desired function outputs are</p> <pre><code>mycmp('1.0', '1') == 0 mycmp('1.0.0', '1') == 0 mycmp('1', '1.0.0.1') == -1 mycmp('12.10', '11.0.0.0.0') == 1 ... </code></pre> <p>And here is my implementation, open for improvement:</p> <pre><code>def mycmp(version1, version2): parts1 = [int(x) for x in version1.split('.')] parts2 = [int(x) for x in version2.split('.')] # fill up the shorter version with zeros ... lendiff = len(parts1) - len(parts2) if lendiff &gt; 0: parts2.extend([0] * lendiff) elif lendiff &lt; 0: parts1.extend([0] * (-lendiff)) for i, p in enumerate(parts1): ret = cmp(p, parts2[i]) if ret: return ret return 0 </code></pre> <p>I'm using Python 2.4.5 btw. (installed at my working place ...).</p> <p>Here's a small 'test suite' you can use</p> <pre><code>assert mycmp('1', '2') == -1 assert mycmp('2', '1') == 1 assert mycmp('1', '1') == 0 assert mycmp('1.0', '1') == 0 assert mycmp('1', '1.000') == 0 assert mycmp('12.01', '12.1') == 0 assert mycmp('13.0.1', '13.00.02') == -1 assert mycmp('1.1.1.1', '1.1.1.1') == 0 assert mycmp('1.1.1.2', '1.1.1.1') == 1 assert mycmp('1.1.3', '1.1.3.000') == 0 assert mycmp('3.1.1.0', '3.1.2.10') == -1 assert mycmp('1.1', '1.10') == -1 </code></pre>
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    1. USJohannes Charra
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    1. CONot an answer but a suggestion -- it might be worth implementing Debian's algorithm for version number comparison (basically, alternating sorting of non-numeric and numeric parts). The algorithm is described [here](http://www.debian.org/doc/debian-policy/ch-controlfields.html) (beginning at "The strings are compared from left to right").
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    2. COBlargh. The subset of markdown supported in comments never fails to confuse me. The link works anyway, even if it looks stupid.
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    3. COIn case future readers need this for user-agent version parsing, I recommend a [dedicated library](http://stackoverflow.com/questions/927552/parsing-http-user-agent-string/10109978#10109978) as the historical variation it too wide.
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      1. USJames Broadhead
 

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