實現一個函數，將一個字符串中的空格替換成“%20”

            
              #!/usr/bin/env python
# -*- coding: utf-8 -*-
test = raw_input()                    # 從鍵盤輸入
inital_length = len(test)
kong = 0                              # kong 用來統計輸入的一行數據中總共有多少個空格
for i in test:
    if i ==" ":
        kong += 1
final_length = inital_length + 2*kong   # 計算轉換后的數組的長度
p1 = inital_length - 1
p2 = final_length - 1
result = [0]*final_length               # 預先設定一個新的數組
if p1 == p2:
    print(test)
while p1 >= 0:                         # 重復此循環直到p1=0
    if test[p1] != " ":
        result[p2] = test[p1]
        p1 = p1-1
        p2 = p2 - 1
    elif test[p1] == " ":
        result[p2] = "0"
        result[p2 - 1] = "2"
        result[p2 - 2] = "%"
        p1 = p1 - 1
        p2 = p2 - 3
convert_str = ''.join(result)       # ''.join()將一個數組轉換為一個字符串
print(convert_str)