Python solution for determining if a function is onto

isOnto

def isOnto(A,B,f):
    x = []
    for i in range(len(f)):
        x.append(f[i][1])
        #print(x)
        i+=1
    B = sorted(B)
    x = list(set(x))
    if B == x:
        return True
    else:
        return False

A = [1, 2, 3]
B = [4, 5]
f = [[1, 4], [2, 5], [3, 4]]
print(isOnto(A, B, f))