Membership of multiple items to a list

[inkhorn]

Dear all,

I'd like to know how to elegantly check a list for the membership of
any of its items to another list.  Not caring for elegance, I would
use the following code:

blah = [1,2,3]
yadda = [3,4,5,6]

blah[0] or blah[1] or blah[2] in yadda

Please tell me how to change the preceding code into something nicer
where I don't have to keep extending the line based on the length of
the first list.

Cheers,
Matt Dubins