python两个列表实例如何相加或相减

import numpy as np
a = [10, 20, 30, 40]
b = [50, 60, 70, 80]
a_np = np.array(a)
b_np = np.array(b)
c_add= a_np + b_np
d_subtract = a_np - b_np
print(c_add)    # [ 60  80 100 120]
print(d_subtract)  #  [-40 -40 -40 -40]