compare two python strings that contain numbers

Question

UPDATE: I should have specified this sooner, but not all of the names are simply floats. For example, some of them are "prefixed" with "YT". So for example" YT1.1. so, you have the same problem YT1.9 < YT1.11 should be true. I'm really surprised that the string comparison fails....

hello, this should be a pretty simple question but I can't seem to find the answer. I'd like to sort a bunch of XL worksheets by name. Each of the names are numbers but in the same way that textbook "sections" are numbered, meaning section 4.11 comes after 4.10 which both come after 4.9 and 4.1. I thought simply comparing these numbers as string would do but I get the following:

>>> s1 = '4.11'
>>> s2 = '4.2'
>>> s1> s2
False
>>> n1 = 4.11
>>> n2 = 4.2
>>> n1 > n2
False

how can I compare these two values such that 4.11 is greater than 4.2?

Answer 1

Convert the names to tuples of integers and compare the tuples:

def splittedname(s):
    return tuple(int(x) for x in s.split('.'))

splittedname(s1) > splittedname(s2)

Update: Since your names apparently can contain other characters than digits, you'll need to check for ValueError and leave any values that can't be converted to ints unchanged:

import re

def tryint(x):
    try:
        return int(x)
    except ValueError:
        return x

def splittedname(s):
    return tuple(tryint(x) for x in re.split('([0-9]+)', s))

To sort a list of names, use splittedname as a key function to sorted:

>>> names = ['YT4.11', '4.3', 'YT4.2', '4.10', 'PT2.19', 'PT2.9']
>>> sorted(names, key=splittedname)
['4.3', '4.10', 'PT2.9', 'PT2.19', 'YT4.2', 'YT4.11']