lists boolean intersect in python ? (SIMPLE)

Hi !

I was wondering: do you know a method to get the common content of 2 lists in python ?

For example:

a=['a','b','c','d']
b=['c','d','e','f']

What i need is a built-in function that return the boolean intersection of a and b, ie [‘c’,‘d’].
Like:

c=listIntersect(a,b)

I have written such a function in about 21 secs, but i was wondering if there wasn’t exactly that somewhere ready.