Python无法以批处理语言打印变量

Question

我想在Python中使用echo打印批处理变量。

from os import system

def CMD(cmd): # this is for do many stuff in one function
    for a in range(0, len(cmd)):
        system(cmd[a])

CMD(["ECHO Hello World!",
     "SET var=Hi!",
     "ECHO %var%", # here i want to print "Hi!" but it prints %var%
     "PAUSE"])

输出：

%var% # i want to get variable: "Hi!"

我如何成功？