求指导！求两个列表的交集（不能用内置函数）

def myintersection():
A=[]
B=[]
C=[]
for i in range (0, len(A)) :
if A[i] in B:
C+=A[i]
return(C)

A=[1,2,3,4,5]
B=[5,6,7]
C=myintersection()
print(C)

def myintersection(A,B):
    C = []
    for i in A:
        if i in B:
            C.append(i)
    return C

A = [1,2,3,4,5]
B = [5,6,7]
C = myintersection(A,B)
print(C)