Validate a nested list and its elements?

[anh193]

I have a validator as follows:
schema = Schema([And(list, lambda x: len(x) == 4)])
Here it validates a list of lists where each child list would have 4 elements.
Question is how should I modify this validator so that it could also verify the elements inside each child list, say they need to be of float type?

[londondaintta]

schema = Schema([And([float], lambda x: len(x) == 4)])