Combinations

def combinations(arr, r):
    for i in range(len(arr)):
        if r == 1:
            yield [arr[i]]
        else:
            for next in combinations(arr[i+1:], r-1):
                yield [arr[i]] + next

for _ in combinations([1,2,3,4,5], 2):
		print(_)

Permutations

def permutations(arr, r):
    for i in range(len(arr)):
        if r == 1:
            yield [arr[i]]
        else:
            for next in permutations(arr[:i] + arr[i+1:], r-1):
                yield [arr[i]] + next

for _ in permutations([1,2,3,4,5], 2):
		print(_)

Combinations_with_replacement

def combinations_with_replacement(arr, r):
    for i in range(len(arr)):
        if r == 1:
            yield [arr[i]]
        else:
            for next in combinations_with_replacement(arr[i:], r-1):
                yield [arr[i]] + next

for _ in combinations_with_replacement([1,2,3,4,5], 2):
		print(_)

Product

def product(arr, r):
    for i in range(len(arr)):
        if r == 1:
            yield [arr[i]]
        else:
            for next in product(arr, r-1):
                yield [arr[i]] + next

for _ in product([1,2,3,4,5], 2):
		print(_)