3字符 → 4字符
83Bite → 46Bite
在 base64 表找对应字符
变表base64
import base64
import string
str1 = "mTyqm7wjODkrNLcWl0eqO8K8gc1BPk1GNLgUpI=="
string1 = "AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0987654321/+"
string2 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
print (base64.b64decode(str1.translate(str.maketrans(string1,string2))))