Recursive code to print samples size of size n

S = []
L = ['a','b','c','d']
N = len(L)
for k1 in range(N):
    if L[k1]:
        S.append(L[k1])
    for k2 in range(N):
        S.append(L[k2])
        for k3 in range(N):
            S.append(L[k3])
            print S
            L[k3] = S.pop()
        L[k2] = S.pop()
    L[k1] = S.pop()

def f(A,B,N):
    if not N:
        print(B)
    else:
        for C in A:
            f(A,B+C,N-1)

print('')
f('abcd','',2)
print('')
f('abcd','',3)
print('')
f('abcd','',5)