Sorting numbers in string format with Python

Programmer Question

I have a list that has some chapter numbers in string.
When I sort the keys using keys function, it gives me wrong results.

keys = ['1.1', '1.2', '2.1', '10.1'] 
keys.sort() 
print keys

['1.1', '1.2', '10.1', '2.1']

How can I use the sort function to get

['1.1', '1.2', '2.1', '10.1']

What if the array has something like this?

['1.1.1', '1.2.1', '10.1', '2.1'] -> ['1.1.1','1.2.1','2.1','10.1']

Find the answer here