Python編程入門到實踐 - 筆記（ 7 章）

第 7 章講了用戶輸入 input( ) 和 while 循環，內容以下

input( ) 工做原理

超過一行的 input( )

int( ) 來獲取數字的輸入，進行比較

求模運算

簡單的 while 循環。我本身的理解就是設定一個條件，while 知足這個條件開始循環，不知足退出

break 直接退出

continue 跳出當前層的循環

避免無限循環

while 在列表中的應用

while 刪除列表中指定的字符串 remove()

用戶輸入的字符來填充字典

input( ) 工做原理

首先定義 input( ) 函數括號中向用戶顯示提示說明，讓用戶輸入內容

在將用戶輸入的內容保存到變量 message 中，最後打印

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message = input("Tell me something, and I will repeat it back to you: ")  
print(message)

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Tell me something, and I will repeat it back to you: haha  
haha

編寫清晰的程序

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name = input("Please enter your name: ")  
print("Hello, " + name + "!")

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Please enter your name: python  
Hello, python!

超過一行的 input

若是想打印多行提示信息，能夠使用 +=

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prompt = "If you tell us who you are, we can personalize the message you see."  
prompt += "\nWhat is your first name? "

name = input(prompt)  
print("\nHello, " + name + "!")

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If you tell us who you are, we can personalize the message you see.  
What is your first name? python

Hello, python!

使用 int( ) 來獲取數值輸入

若是不指定 age=int(age)，python將會報錯

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age = input("How old are you? ")  
print(age)

age = int(age)

if age >= 18:  
     print(age)

-------------------------------------------

How old are you? 29  
29    
29

 

int( ) 進行數值比較，進行測試

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height = input("How tall are you, in inches? ")  
height = int(height)

if height >= 36:  
     print("\nYou're tall enough to ride!")    
else:    
     print("\nYou'll be able to ride when you're a little older.")

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How tall are you, in inches? 89

You're tall enough to ride!

求膜運算符

兩個數相除，返回餘數

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print(4 % 3)  
print(5 % 3)    
print(6 % 3)    
print(7 % 3)

----------------------

1  
2    
0    
1

能夠利用求模來計算一個數是奇數仍是偶數

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number = input("Enter a number, and I'll tell you if it's even or odd: ")  
number = int(number)

if number % 2 == 0:  
     print("\nThe number " + str(number) + " is even.")    
else:    
     print("\nThe number " + str(number) + " is odd.")

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Enter a number, and I'll tell you if it's even or odd: 78

The number 78 is even.

while 循環

若是 while 小於等於 5，就一直運行

打印一次後，就將 current_number 的數值 +1

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current_number = 1  
while current_number <= 5:    
     print(current_number)    
     current_number += 1

--------------------------------------

1  
2    
3    
4    
5

讓用戶選擇什麼時候退出

若是用戶不輸入 quit，就一直循環下去

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prompt = "\nTell me something, and I will repeat it back to you:"  
prompt += "\nEnter 'quit' to end the program. "    
message = ""

while message != 'quit':  
     message = input(prompt)    
     print(message)

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Tell me something, and I will repeat it back to you:  
Enter 'quit' to end the program. zhao    
zhao

Tell me something, and I will repeat it back to you:  
Enter 'quit' to end the program. shanshan    
shanshan

Tell me something, and I will repeat it back to you:  
Enter 'quit' to end the program. quit    
quit

進行更改

上面的程序在用戶輸入 quit 時，也會將 quit 做爲消息在打印一遍

代碼中並無定義若是用戶輸入 quit 會怎麼樣，因此當用戶輸入 quit

直接結束循環，退出

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prompt = "\nTell me something, and I will repeat it back to you:"  
prompt += "\nEnter 'quit' to end the program. "    
message = ""

while message != 'quit':  
     message = input(prompt)

     if message != 'quit':  
          print(message)

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Tell me something, and I will repeat it back to you:  
Enter 'quit' to end the program. zhao    
zhao

Tell me something, and I will repeat it back to you:  
Enter 'quit' to end the program. quit

繼續改進上面的代碼

就像剛纔說的，並無指定若是用戶輸入 quit 會怎麼樣

其實在 while 循環中嵌套一個 if-else 語句就能夠了

可是開始循環時，先定義一個 active=True

若是是 True 就循環，是 False 就中止循環

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prompt = "\nTell me something, and I will repeat it back to you:"  
prompt += "\nEnter 'quit' to end the program. "

active = True  
while active:    
     message = input(prompt)

     if message == 'quit':  
          active = False    
     else:    
          print(message)

------------------------------------------------------------------------------------

Tell me something, and I will repeat it back to you:  
Enter 'quit' to end the program. zhao    
zhao

Tell me something, and I will repeat it back to you:  
Enter 'quit' to end the program. quit

break 直接退出循環

仍是以上面的代碼爲例，當用戶輸入 break 時，直接 break，結束當前的 while 循環

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prompt = "\nPlease enter the name of a city you have visited:"  
prompt += "\n(Enter 'quit' when you are finished.)"

while True:  
     city = input(prompt)

     if city == 'quit':  
          break    
     else:    
          print("I'd love to go to " + city.title() + "!")

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Please enter the name of a city you have visited:  
(Enter 'quit' when you are finished.)zhao    
I'd love to go to Zhao!

Please enter the name of a city you have visited:  
(Enter 'quit' when you are finished.)shushu    
I'd love to go to Shushu!

Please enter the name of a city you have visited:  
(Enter 'quit' when you are finished.)quit

continue 跳出當前的循環

每循環一次就 +1，當 current_number 能夠被 2 整除的時候

就執行 continue，跳出這一層循環，繼續 while 的下一次循環

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current_number = 0  
while current_number < 10:    
     current_number += 1    
      if current_number % 2 == 0:    
          continue

     print(current_number)

------------------------------------------

1  
3    
5    
7    
9

避免無限循環

死循環代碼以下，x 開始等於 1，在第一次循環結束後並無變，

一直等於 1，永遠知足  x <= 5 的條件，因此會被一直打印

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x = 1  
while x <= 5:    
     print(x)

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正常代碼

須要指定一個條件，每循環一次 x 的值都 +1

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x = 1  
while x <= 5:    
     print(x)    
     x += 1

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while 在列表中的應用

-----------------------------------------------------------------------

unconfirmed_users = ['alice', 'brian', 'candace']  
confirmed_users = []

while unconfirmed_users:  
     current_user = unconfirmed_users.pop()

     print("Verifying user: " + current_user.title())  
     confirmed_users.append(current_user)    
    
print("\nThe following users have been confirmed:")    
for confirmed_user in confirmed_users:    
     print(confirmed_user.title())

-----------------------------------------------------------------------

Verifying user: Candace  
Verifying user: Brian    
Verifying user: Alice

The following users have been confirmed:  
Candace    
Brian    
Alice

刪除包含特定值的全部列表元素

while 中一直執行 remove( ) 刪除列表中的 cat 字符

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pets = ['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']  
print(pets)

while 'cat' in pets:  
     pets.remove('cat')

print(pets)

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['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']  
['dog', 'dog', 'goldfish', 'rabbit']

用戶輸入來填充字典

定義一個空的字典 responses

定義 polling_active = True 開始循環，等於 False 退出循環

讓用戶分別輸入 name，response

responses[name] = response  將用戶輸入的添加到 responses 字典中

for 循環 items( ) 遍歷 responses 字典

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responses = {}

polling_active = True

while polling_active:  
     name = input("\nWhat is your name? ")    
     response = input("Which mountain would you like to climb someday? ")

     responses[name] = response

     repeat = input("Would you like to let another person respind? (yes/ no) ")  
     if repeat == 'no':    
          polling_active = False

print("\n--- Poll Results ---")  
for name, response in responses.items():    
     print(name + " would like to climb " + response + ".")

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What is your name? shanshan  
Which mountain would you like to climb someday? taiqiu    
Would you like to let another person respind? (yes/ no) no

--- Poll Results ---   shanshan would like to climb taiqiu .