Version number comparison in Python

Question

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

user_4144446 · Answer

i'm using this one on my project:

cmp(v1.split("."), v2.split(".")) >= 0

user_9935708 · Answer

Years later, but stil this question is on the top.

Here is my version sort function. It splits version into numbers and non-numbers sections. Numbers are compared as int rest as str (as parts of list items).

def sort_version_2(data):
    def key(n):
        a = re.split(r'(\d+)', n)
        a[1::2] = map(int, a[1::2])
        return a
    return sorted(data, key=lambda n: key(n))

You can use function key as kind of custom Version type with compare operators. If out really want to use cmp you can do it like in this example: https://stackoverflow.com/a/22490617/9935708

def Version(s):
    s = re.sub(r'(\.0*)*$', '', s)  # to avoid ".0" at end
    a = re.split(r'(\d+)', s)
    a[1::2] = map(int, a[1::2])
    return a

def mycmp(a, b):
    a, b = Version(a), Version(b)
    return (a > b) - (a < b)  # DSM's answer

Test suite passes.

Version number comparison in Python

17 Answers