Just how random is it possible for Python to be?

If I am starting with a list of hundreds or perhaps thousands of separate items, and I want Python to choose one (at a time) at random (for creating a ciphertext), how "random" will it really be? It's highly important that there be no repeats of the same item (integers, strings) whatsoever, because of the crypt0graphic nature of the app. But is there some way to confidently perform random selection from dictionaries?