Python3 参考方法：

#!/usr/bin/python3

def f8to10(num):
    print("8进制数：", num)
    l = str(num)
    length = len(l)
    sum = 0
    for i in range(length):
        sum += 8 ** i * int(l[length-1-i])
    print("转成10进制数为：",sum)

f8to10(122)

参考方法：

#!/usr/bin/python
# -*- coding: UTF-8 -*-

def batoshi(num):
    count=0
    j=len(num)-1
    for each_ch in num:
        count+=pow(8,j)*int(each_ch)
        j-=1
    return count

print(batoshi('122'))

参考方法：

#coding=utf-8

n = reversed('122')

s = 0
for idx,i in enumerate(n):
    s += int(i) * pow(8, idx)
print (s)