#Strings (and numbers and tuples) are immutable: you can't modify them.
def change(n):
n[0] = 'Changed'
names = ['A', 'B']
change(names)
print names
names = ['A', 'B']
n = names # Again pretending to pass names as a parameter
n[0] = 'Changed' # Change the list
print names
names = ['A', 'B']
n = names[:]
print n is names
print n == names
n[0] = 'Changed'
print n
print names
change(names[:])
print names