import random

def gen_randoms(how_many, max_val):
    L = []
    #D = {}
    for i in range(how_many):
        val = random.randint(0, max_val)
        L.append(val)
        #D[val] = D.setdefault(val, 0) + 1
    #return D
    return L

def count_randoms(L1, L2):
    count = 0
    for x in L1:
        if x in L2: count += 1
        # note: if L2 is a list then "x in L2" does a loop and checks every
        #  single item in L2
    return count

n = 10*10**4
m = n * 1000
L1 = gen_randoms(n, m)
L2 = gen_randoms(n, m)
#print(L1)
#print(L2)

print(count_randoms(L1, L2))