python程式設計：從入門到實踐學習筆記-使用者輸入和while迴圈

嗨學程式設計發表於2018-11-05
Python程式設計筆記While

python程式設計：從入門到實踐學習筆記-使用者輸入和while迴圈

函式input()

input() ：暫停程式，等待使用者輸入文字並把文字儲存在指定變數中。並接受一個引數，即要向使用者顯示的提示或說明。
int() ：使用input()函式時，輸入的文字會被當成字串，所以可以用這個函式將其化為int型。
% ：求模運算子。講兩個數相除並返回餘數。
下面舉個例子：

message = input("Tell me your name:")
print(message) 
message = input("Tell me your years:")
if int(message) >= 18:
    print('wow')
    print(int(message) % 6)

#執行結果：
Tell me your name:mike
mike
Tell me your years:19
wow
1複製程式碼

while迴圈

迴圈簡介
while迴圈不斷執行，直到指定的條件不滿足位置。例如：

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

#執行結果：
1
2
3
4
5複製程式碼

還可以讓使用者選擇何時退出，只要把迴圈的條件由current_number <= 5改為message != 'quit'，然後在迴圈語句裡面新增message = input(prompt)，即：

current_number = 1
while message != 'quit':
    message = input('Enter 'quit' to end the program or go on:')
    print(current_number)
    current_number += 1 

#執行結果：
Enter 'quit' to end the program or go on: 
1
Enter 'quit' to end the program or go on: 
2
Enter 'quit' to end the program or go on:quit複製程式碼

這時候我們提示了一條訊息：要麼輸入quit來結束程式，要麼繼續執行。當然我們還可以設定標誌來決定迴圈的條件，比如利用布林值True或者False。

退出迴圈
break ：不管條件測試結果如何，立即退出迴圈，不在執行迴圈中餘下程式碼。

prompt = "\nPlease enter a city you have visited:"
prompt += "\n(Enter 'quit' when you are finished.) "
while True:
    city = input(prompt)
    if city == 'quit':
        break 

#執行結果：
Please enter a city you have visited:
(Enter 'quit' when you are finished.) China
I'd love to go to China!

Please enter a city you have visited:
(Enter 'quit' when you are finished.) San Francisco
I'd love to go to San Francisco!

Please enter a city you have visited:
(Enter 'quit' when you are finished.) quit複製程式碼

continue ：跳出此次迴圈，即返回到迴圈開頭，並判斷迴圈條件是否滿足來決定是否執行迴圈。

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

#執行結果：
1
3
5
7
9複製程式碼

使用迴圈處理列表和字典

for迴圈中不應修改列表，因為for迴圈中修改列表之後，python的遍歷會出現問題。而要想遍歷列表並修改，可以用while迴圈。下面舉幾個例子。

在列表之間移動元素

#建立待驗證使用者列表和一個已驗證使用者列表
unconfirmed_ids = ['mike', 'lili', 'ace']
confirmed_ids = [] 
#驗證每個使用者並把其移動到已驗證使用者列表
while unconfirmed_ids:
    current_id = unconfirmed_ids.pop()
    print("Verifying id: " + current_id.title())
    confirmed_ids.append(current_id)

#顯示所有已驗證id
print("\nThe following ids have been confirmed:")
for confirmed_id in confirmed_ids:
    print(confirmed_id.title()) 

#執行結果：
Ace
Lili
Mike複製程式碼

刪除包含特定值的所有列表元素

nums = ['1', '3', '5', '1', '6', '1', '7']
print(nums)
while '1' in nums:
    pets.remove('1')
print(nums)

#執行結果：
['3', '5', '6', '7']複製程式碼

使用使用者輸入來填充字典

responses = {}
#設定一個標誌Lj指出調查是否繼續
polling_active = True
while polling_active:
    #提示輸入被調查者的名字和回答
    name = input("\nWhat is your name? ")
    response = input("Which mountain would you like to climb someday? ")

    #將答卷儲存在字典中
    responses[name] = response

    #看看是否有人要參與調查
    repeat = input("Would you like to let another person respond? (yes/ no) ")
    if repeat == 'no':
        polling_active = False

#調查結束顯示結果
print("\n--- Poll Results ---")
for name, response in responses.items():
    print(name + " would like to climb " + response + ".") 

#執行結果：
What is your name? Eric
Which mountain would you like to climb someday? Denali
Would you like to let another person respond? (yes/ no) yes

What is your name? Lynn
Which mountain would you like to climb someday? Devil's Thumb
Would you like to let another person respond? (yes/ no) no

--- Poll Results ---
Lynn would like to climb Devil's Thumb.
Eric would like to climb Denali.複製程式碼


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