How do I lowercase a string in Python?

Also, you can overwrite some variables:

s = input('UPPER CASE')
lower = s.lower()

If you use like this:

s = "Kilometer"
print(s.lower())     - kilometer
print(s)             - Kilometer

It will work just when called.

Don't try this, totally un-recommend, don't do this:

import string
s='ABCD'
print(''.join([string.ascii_lowercase[string.ascii_uppercase.index(i)] for i in s]))

Output:

abcd

Since no one wrote it yet you can use swapcase (so uppercase letters will become lowercase, and vice versa) (and this one you should use in cases where i just mentioned (convert upper to lower, lower to upper)):

s='ABCD'
print(s.swapcase())

Output:

abcd