今天介紹另一個循環判斷式 for循環，首先，先寫一個很簡單的 for循環的代碼

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

for i in range(10):
    print("loop:", i)
    
---------------執行結果---------------

loop: 0
loop: 1
loop: 2
loop: 3
loop: 4
loop: 5
loop: 6
loop: 7
loop: 8
loop: 9

Process finished with exit code 0

那 for循環是怎麼跑的呢？請看下圖

接下來我們再來延伸一下，如果我想要把一開始的 form循環 每隔一個數字才打印出來，要怎麼實現？

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

for i in range(0, 10, 2):
    print("loop:", i)
    
---------------執行結果---------------

loop: 0
loop: 2
loop: 4
loop: 6
loop: 8

Process finished with exit code 0

這樣就可以達成目的了，接下來要再提升一點難度，如何把 for循環 判斷式套用到猜年紀的遊戲中呢？忘記了請參考Python 基礎 - while流程判斷 的最後一個代碼

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

age_of_ironman = 35

for i in range(3):
    guess_age = int(input("guess age:"))
    if guess_age == age_of_ironman:
        print("Bingo, You got it!!!")
        break
    elif guess_age > age_of_ironman:
        print("You may think smaller...")
    else:
        print("You may think bigger...")
else:
    print("You have tried too many, exit")

---------------執行結果---------------

# 故意猜超過三次，看看結果
guess age:1
You may think bigger...
guess age:2
You may think bigger...
guess age:3
You may think bigger...
You have tried too many, exit

Process finished with exit code 0

# 先試試在三次內打對密碼，看看結果
guess age:4
You may think bigger...
guess age:35
Bingo, You got it!!!

Process finished with exit code 0

上面的代碼因為用了 for循環 就不需要計數器了，因此就把 count = 0 跟 count += 1 給刪除了，就可以完成了，但是這段代碼的 for循環 又是怎麼跑的呢？請看下圖

再來再提升一下難度，這次需求是要讓這個遊戲可以讓任隨便玩，不過一樣要每三次問一下，要不要繼續玩？

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

age_of_ironman = 35

count = 0

while count < 3:
    guess_age = int(input("guess age:"))
    if guess_age == age_of_ironman:
        print("Bingo, You got it!!!")
        break
    elif guess_age > age_of_ironman:
        print("You may think smaller...")
    else:
        print("You may think bigger...")
    count += 1
    if count == 3:
        countine_confirm = input("Do you want to keep go in ? (y/n)")
        if countine_confirm != 'n':
            count = 0
else:
    print("You have tried too many, exit")

---------------執行結果---------------

# 故意猜錯三次，第二次詢問時，選n
guess age:1
You may think bigger...
guess age:2
You may think bigger...
guess age:3
You may think bigger...
Do you want to keep go in ? (y/n)
guess age:4
You may think bigger...
guess age:5
You may think bigger...
guess age:6
You may think bigger...
Do you want to keep go in ? (y/n)n
You have tried too many, exit

Process finished with exit code 0

有發現上面代碼有一個怪怪的地方嗎？請看下圖說明

所以我們只要把需要註解或是刪除那二碼代碼即可

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

age_of_ironman = 35

count = 0

while count < 3:
    guess_age = int(input("guess age:"))
    if guess_age == age_of_ironman:
        print("Bingo, You got it!!!")
        break
    elif guess_age > age_of_ironman:
        print("You may think smaller...")
    else:
        print("You may think bigger...")
    count += 1
    if count == 3:
        countine_confirm = input("Do you want to keep go in ? (y/n)")
        if countine_confirm != 'n':
            count = 0

---------------執行結果---------------

# 故意猜錯三次，第二次詢問時，選n
guess age:1
You may think bigger...
guess age:2
You may think bigger...
guess age:3
You may think bigger...
Do you want to keep go in ? (y/n)y
guess age:4
You may think bigger...
guess age:5
You may think bigger...
guess age:6
You may think bigger...
Do you want to keep go in ? (y/n)n

Process finished with exit code 0

知識點：

• 語法：range(start, stop[, step]) 裡面的 step 預設是 1

參考資料：

• why the python use 0-based