Python - Ignore letter case

Question

I have an if statement:

rules = input ("Would you like to read the instructions? ")
rulesa = "Yes"
if rules == rulesa:
    print  ("No cheating")
else: print ("Have fun!")

I wish for the user to be able to answer with Yes, YES, yES, yes or any other capitalisation, and for the code to know that they mean Yes.

Answer 1

For this simple example you can just compare lowercased rules with "yes":

rules = input ("Would you like to read the instructions? ")
rulesa = "yes"
if rules.lower() == rulesa:
    print  ("No cheating")
else: 
    print ("Have fun!")

It is OK for many cases, but be awared, some languages may give you a tricky results. For example, German letter ß gives following:

"ß".lower() is "ß"
"ß".upper() is "SS"
"ß".upper().lower() is "ss"
("ß".upper().lower() == "ß".lower()) is False

So we may have troubles, if our string was uppercased somewhere before our call to lower(). Same behaviour may also be met in Greek language. Read the post https://stackoverflow.com/a/29247821/2433843 for more information.

So in generic case, you may need to use str.casefold() function (since python3.3), which handles tricky cases and is recommended way for case-independent comparation:

rules.casefold() == rulesa.casefold()

instead of just

rules.lower() == rulesa.lower()