["python","string-comparison"]
Version number comparison in Python

I want to write a cmp-like function that compares two version numbers and returns -1, 0, or 1 based on their compared values. Return -1 if version A is older than version B Return 0 if versions A and B are equivalent Return 1 if version A is newer than version B Each subsection is supposed to be interpreted as a number, therefore 1.10 > 1.1. Desired function outputs are 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 ... And here is my implementation, open for improvement: 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 > 0: parts2.extend([0] * lendiff) elif lendiff < 0: parts1.extend([0] * (-lendiff)) for i, p in enumerate(parts1): ret = cmp(p, parts2[i]) if ret: return ret return 0 I'm using Python 2.4.5 btw. (installed at my working place ...). Here's a small 'test suite' you can use 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
Remove the uninteresting part of the string (trailing zeroes and dots), and then compare the lists of numbers. import re def mycmp(version1, version2): def normalize(v): return [int(x) for x in re.sub(r'(\.0+)*$','', v).split(".")] return cmp(normalize(version1), normalize(version2)) This is the same approach as Pär Wieslander, but a bit more compact: Here are some tests, thanks to "How to compare two strings in dot separated version format in Bash?": assert mycmp("1", "1") == 0 assert mycmp("2.1", "2.2") < 0 assert mycmp("3.0.4.10", "3.0.4.2") > 0 assert mycmp("4.08", "4.08.01") < 0 assert mycmp("3.2.1.9.8144", "3.2") > 0 assert mycmp("3.2", "3.2.1.9.8144") < 0 assert mycmp("1.2", "2.1") < 0 assert mycmp("2.1", "1.2") > 0 assert mycmp("5.6.7", "5.6.7") == 0 assert mycmp("1.01.1", "1.1.1") == 0 assert mycmp("1.1.1", "1.01.1") == 0 assert mycmp("1", "1.0") == 0 assert mycmp("1.0", "1") == 0 assert mycmp("1.0", "1.0.1") < 0 assert mycmp("1.0.1", "1.0") > 0 assert mycmp("1.0.2.0", "1.0.2") == 0