How does __setitem__() work?

[Bob Erb]

Given the following class definition,

class Test:
    
    def __setattr__(self, attribute, value):
        print 'setting', attribute, 'to', value
        self.__dict__[attribute] = value
    
    def __setitem__(self, index, value):
        print 'setting index', index, 'to', value
        ## THE_BLANK

I have two questions.

First, when is __setitem__ called? __setattr__() is
called when I do:

>>> t = Test(); t.list = [1,2,3]
setting list to [1, 2, 3]

I expected __setitem__ to be called when I do:

>>> t.list[0] = 7

That doesn't happen; when does __setitem__ get
called?

My second question is, to pass the assignment in
__setitem__ through, what code goes in 'THE_BLANK'
above?

(What I'm trying to do is ensure that the value of
a variable is a certain type. For instance, I want
to disallow assignment of a string value to an
integer variable. Is this anti-Python?)

Thanks for any help.

 - Bob Erb