If…else的进阶，用几个程序来实现讲解。
用if猜数字：
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#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind
age = 56
guess_age = int(input("guess age:"))
if guess_age == age:
print("yes, you got it.")
elif guess_age > age:
print("think smaller...")
else:
print("think bigger...")
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输出：
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guess age:23
think bigger...
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解释：
如要需要判断多个条件，在if…else中添加elif，需要多少添加多少，如上文程序。
但是，这样程序只能执行一次就结束了，加入次数条件控制（程序的循环执行）。
while实现循环：
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#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind
count = 0
while True:
print("count:", count)
count = count + 1 #count += 1
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输出：
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count: 102609
count: 102610
count: 102611
count: 102612…
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解释：
while条件为真（True永远为真），代码块就一直执行（程序无限执行）。（程序中count +=1与count = count + 1是等价的）。
加入while条件循环的猜数字：
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#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind
age = 56
while True:
guess_age = int(input("guess age:"))
if guess_age == age:
print("yes, you got it.")
elif guess_age > age:
print("think smaller...")
else:
print("think bigger...")
|
输出：
|
guess age:56
yes, you got it.
guess age:23
think bigger...
|
解释：
无论猜对错，程序无限执行，不好，改进一下：
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#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind
age = 56
while True:
guess_age = int(input("guess age:"))
if guess_age == age:
print("yes, you got it.")
break
elif guess_age > age:
print("think smaller...")
else:
print("think bigger...")
|
输出：
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guess age:67
think smaller...
guess age:56
yes, you got it.
Process finished with exit code 0
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解释：
break：退出，结束循环。
此时程序猜对退出执行，但猜错的话还是无限猜下去，还是不好，再改进：
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#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind
age = 56
count = 0
while True:
if count == 3:
break
guess_age = int(input("guess age:"))
if guess_age == age:
print("yes, you got it.")
break
elif guess_age > age:
print("think smaller...")
else:
print("think bigger...")
count += 1
|
输出：
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guess age:1
think bigger...
guess age:2
think bigger...
guess age:3
think bigger...
Process finished with exit code 0
|
解释：
程序猜对，或者猜错三次结束执行，但是还是很low：
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#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind
age = 56
count = 0
while count < 3:
guess_age = int(input("guess age:"))
if guess_age == age:
print("yes, you got it.")
break
elif guess_age > age:
print("think smaller...")
else:
print("think bigger...")
count += 1
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程序稍好看一点点，输出略，同上一个代码是一样的功能，下面while再添加一个else
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#!/usr/bin/env python
# -*- coding:utf-8 -*-
#Author:Mclind
age = 56
count = 0
while count < 3:
guess_age = int(input("guess age:"))
if guess_age == age:
print("yes, you got it.")
break
elif guess_age > age:
print("think smaller...")
else:
print("think bigger...")
count += 1
else:
print("you have tried too many times... fuck off")
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输出：
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guess age:1
think bigger...
guess age:2
think bigger...
guess age:3
think bigger...
you have tried too many times... fuck off
Process finished with exit code 0
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解释：
输入错误三次才打印print语句，while后可以接else语句，意思是如果while都正常走完了，那么执行else后的代码块，否则（如break结束循环了）就不再执行else后的代码块。
