How to sort a list of strings numerically?


I know that this sounds trivial but I did not realize that the sort() function of Python was weird. I have a list of "numbers" that are actually in string form, so I first convert them to ints, then attempt a sort.

for item in list1:

print list1

Gives me:

['1', '10', '2', '200', '22', '23', '3', '4']

What I want is


I've looked around for some of the algorithms associated with sorting numeric sets, but the ones I found all involve sorting alphanumeric sets.

I know this is probably a no brainer problem but google and my textbook don't offer anything more or less useful than the .sort() function.

4/1/2019 4:18:12 PM

Accepted Answer

You haven't actually converted your strings to ints. Or rather, you did, but then you didn't do anything with the results. What you want is:

list1 = ["1","10","3","22","23","4","2","200"]
list1 = [int(x) for x in list1]

If for some reason you need to keep strings instead of ints (usually a bad idea, but maybe you need to preserve leading zeros or something), you can use a key function. sort takes a named parameter, key, which is a function that is called on each element before it is compared. The key function's return values are compared instead of comparing the list elements directly:

list1 = ["1","10","3","22","23","4","2","200"]
# call int(x) on each element before comparing it
5/12/2019 10:24:44 PM

You could pass a function to the key parameter to the .sort method. With this, the system will sort by key(x) instead of x.


BTW, to convert the list to integers permanently, use the map function

list1 = list(map(int, list1))   # you don't need to call list() in Python 2.x

or list comprehension

list1 = [int(x) for x in list1]

Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow