from itertools import combinations, permutations, product, groupby

print(list(combinations("ABC", 2)))
print(len(list(permutations("ABC"))))
print(list(product([1, 2], "xy")))

words = ["apple", "avocado", "banana", "blueberry", "cherry"]
for letter, group in groupby(words, key=lambda w: w[0]):
    print(letter, list(group))

combinations(items, r): every way to choose r items, order not mattering.
permutations(items): every ordering.
product(a, b): every pair, like a nested loop.
groupby(items, key): groups neighbouring items with the same key. The data must already be sorted by that key for it to group everything together.