Changing argument value

[flyfree]

>>> def fooA(y):
	y = [3,4]
	return y

>>> def fooB(y):
	y[0] = 3
	y[1] = 4
	return y

>>> x = [1,2]
>>> fooA(x)
[3, 4]
>>> x
[1, 2]

>>> fooB(x)
[3, 4]
>>> x
[3, 4]
===============

>From above, the original argument value of fooA is same as before
[1,2]
but the original argument value of fooB is changed from [1,2] to
[3,4].

What is the difference between "y = [3,4]" and "y[0]=3
 
y[1] =4 "


Thanks,

SC