Is a string higher than another string in Python 3?

Question

Workout if a string holding a version number is higher than another string holding a version number in Python 3.

This is what I have tried:

request_version = "1.10.1"
current_version = "1.11"
if Decimal(request_version) > Decimal(current_version):
    pass

However, I get this error, why?

InvalidOperation at /api/version/
[<class 'decimal.ConversionSyntax'>]

Nope, works fine: https://repl.it/BteN. Are you sure you're not trying to take a patch release (e.g. `1.2.3`) or something? Also, note that releases don't compare numerically - `1.2` is less recent than `1.11`, even though it's a larger number, for example. — jonrsharpe, Mar 07 '16 at 11:45
Well then: 1. The answer is obvious (*"why?"* - because `1.10.1` isn't a valid number); and: 2. You're still going to hit the problem that comparing them as numbers is precisely the wrong way to do this. — jonrsharpe, Mar 07 '16 at 11:47
Version strings are not decimal numbers! Use functions specialised in comparing version strings. — deceze, Mar 07 '16 at 11:47
Could you help and provide an answer on how I could compare these? — Prometheus, Mar 07 '16 at 11:48
In terms of how to correctly compare version numbers, see e.g. http://semver.org/. In terms of implementation, write your own homework! — jonrsharpe, Mar 07 '16 at 11:49

score 4 · Accepted Answer · answered Mar 07 '16 at 11:54

You're trying to convert your version string to a float, which fails because 1.2.3 is not a valid float.

What you probably want for this kind of things is the packaging package, which implements the PEP 440 version semantics (among other niceties):

>>> from packaging.version import parse
>>> request_version = parse("1.10.1")
>>> current_version = parse("1.11")
>>> request_version > current_version
False
>>> request_version < current_version
True

This parse will create a Version object, which allows comparison between versions

score 1 · Answer 2 · answered Mar 07 '16 at 11:58

1

You might want to use LooseVersion from distutils.version:

from distutils.version import LooseVersion as V

current = V('1.10.1')
request_version = V('1.11')

if current < request_version:
    print("Yay.")

answered Mar 07 '16 at 11:58

ferdy

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Is a string higher than another string in Python 3?

2 Answers2