Sorting a list of strings numerically

Question

I have a list of strings with my filenames:

flist = ['0.png','10.png', '3.png', '4.png', '100.png']
flist.sort()
print(flist)

Output:

['0.png', '10.png', '100.png', '3.png', '4.png']

But I want:

['0.png', '3.png', '4.png', '10.png', '100.png']

Is there a simple way to do this?

Answer 1

Yes:

flist.sort(key=lambda fname: int(fname.split('.')[0]))

Explanation: strings are lexically sorted so "10" comes before "3" (because "1" < "3", so whatever comes after "1" in the first string is ignored). So we use list.sort()'s key argument which is a callback function that takes a list item and return the value to be used for ordering for this item - in your case, an integer built from the first part of the filename. This way the list is properly sorted on the numerical values.