import numpy as np
# 本当は10万くらいの長さ
a = np.array([[1,2,3],[4,5,6],[7,8,9]])
# こっちも10万くらいの長さ
b = np.array([ [ [1,2,3],[4,5,6],[7,8,9] ], [ [1,2,3],[4,5,6],[7,8,9] ] ])
res = []
for i in range(a.shape[0]):
    for j in range(b.shape[0]):
        c = np.dot(a[i],b[j])
        res.append(c)