When you try to sort a list of strings that contain numbers, the
normal python sort algorithm sorts lexicographically, so you might
not get the results that you expect:

>>> a = ['a2', 'a9', 'a1', 'a4', 'a10']
>>> sorted(a)
['a1', 'a10', 'a2', 'a4', 'a9']

Notice that it has the order ('1', '10', '2') - this is because the
list is being sorted in lexicographical order, which sorts numbers
like you would letters (i.e. 'b', 'ba', 'c').

natsort provides a function natsorted that helps sort lists
"naturally", either as real numbers (i.e. signed/unsigned floats
or ints), or as versions. Using natsorted is simple:

>>> from natsort import natsorted
>>> a = ['a2', 'a9', 'a1', 'a4', 'a10']
>>> natsorted(a)
['a1', 'a2', 'a4', 'a9', 'a10']

natsorted identifies numbers anywhere in a string and sorts them
naturally.