Do anyone know why i got this error ? Do i have to import anything in order to use string.lower() & string.upper() ?

sentence = "how are you"
newS = string.lower(sentence)
NameError: name 'string' is not defined

There are two ways to do this ...

# older way, needs to import string module
import string

sentence = "HOW ARE YOU"
newS = string.lower(sentence)
print newS

# newer way, no import needed
newerS = sentence.lower()
print newerS

Why i got this error ?

newS = sentence.lower()
AttributeError: 'tuple' object has no attribute 'lower'

The only way I can recreate this error is to make variable sentence a tuple ...

#sentence = "HOW ARE YOU"
sentence = 'HOW', 'ARE', 'YOU'
newS = sentence.lower()
print newS

Are you using an older version of Python?