Python 學習筆記8 循環語句 while

While循環是喲中利用條件語句，不斷的執行某一段代碼塊，達到批量操做輸出等一系列的操做，直到條件不知足或者被強制退出爲止。

其工做流程以下： （圖片來源菜鳥教程：http://www.runoob.com/python/python-while-loop.html  ）

 

咱們來看一個例子：

current_number = 10
while current_number <= 20:
    print("Current number is : " + str(current_number))
    current_number += 1

print("Final number: " + str(current_number))

'''
輸出：
Current number is : 10
Current number is : 11
Current number is : 12
Current number is : 13
Current number is : 14
Current number is : 15
Current number is : 16
Current number is : 17
Current number is : 18
Current number is : 19
Current number is : 20 
Final number: 21
'''

 

咱們能夠看到 變量current_number 的初始值爲10， 在小於等於20的狀況下，不斷的被打印，被增加，直至增加到21的時候，跳出了循環。

咱們也能夠使用標誌，好比True,False 等布爾值來進行循環：

flag = True
while flag:
    number = int(input("Input a number less than 10:\n"))
    if number < 10:
        flag = True
    else:
        flag = False

print("The game is end...")

'''
輸出：
Input a number less than 10:
2
Input a number less than 10:
11
The game is end...
Final number: 21
'''

 

使用 break 退出循環。在while循環中，你能夠經過特定的條件語句，選擇終止循環，再也不繼續運行餘下的代碼。

flag = True
while flag:
    city = input("Input a city which you like: \n" + "Input 'Q' to quit...\n")
    if city == 'Q':
        break
    else:
        print("You like " + city)

print("Thanks for your information.")

'''
輸出：
Input a city which you like: 
Input 'Q' to quit...
ShangHai
You like ShangHai
Input a city which you like: 
Input 'Q' to quit...
HangZhou
You like HangZhou
Input a city which you like: 
Input 'Q' to quit...
Q
Thanks for your information.
'''

 

使用 continue 再也不繼續執行餘下的代碼塊，返回到循環開頭，繼續下一輪循環。

number = 0
while number <= 10:
    if number % 2 == 0:
        print("The number is even: " + str(number))
        number += 1
        continue
        print("Next...")
    else:
        number += 1



'''
輸出：
The number is even: 0
The number is even: 2
The number is even: 4
The number is even: 6
The number is even: 8
The number is even: 10
'''

 循環也能夠和else 一塊兒使用：

number = 0
while number <= 10:
    if number % 2 == 0:
        print("The number is even: " + str(number))
        number += 1
        continue
        print("Next...")
    else:
        number += 1
else:
    print("The number is equal or more than 10, stop loop.")


'''
輸出：
The number is even: 0
The number is even: 2
The number is even: 4
The number is even: 6
The number is even: 8
The number is even: 10
The number is equal or more than 10, stop loop.
'''

 

使用while 操做列表 List

peoples = ['Ralf', 'Clark', 'Leon']
while peoples:
    people = peoples.pop()
    print(people)

'''
輸出：
Leon
Clark
Ralf
'''

peoples = ['Ralf', 'Clark', 'Leon', 'Terry']
while 'Terry' in peoples:
    peoples.remove('Terry')
    print(peoples)

'''
輸出：
['Ralf', 'Clark', 'Leon']
'''

 

while循環語句能夠解決程序中須要重複執行的操做。其循環執行的次數由循環條件肯定，當循環條件知足時，重複執行某程序段，直到循環條件不成立爲止。反覆執行的程序段稱爲循環體，循環條件必需要在循環體中改變，不然可能會出現無限循環的結果