How to convert upper case letters to lower case [duplicate]

I have a script which reads the input and than lists it, however i want it to convert upper case letters to lower case, how can i do that?

this is what i got

 for words in text.readlines():
    sentence = [w.strip(',.') for w in line.split() if w.strip(',.')]
    list.append(sentence)

Solution 1:

You can find more methods and functions related to Python strings in section 5.6.1. String Methods of the documentation.

w.strip(',.').lower()

str.lower() converts all cased characters to lowercase.