在while循環中分配後只有兩個變量

Question

當我運行代碼時，它要求用戶輸入3次，但是當條件滿足時，它仍然只打印其中的2個。爲什麼？我對Python很陌生，但在谷歌上看到任何答案都很瘋狂，但我仍然感到困惑。

name = raw_input("Name your age: ") 
print ("3 choices.") 
key = raw_input("What will this world have?: ") 

def generator(): 
    data = 1 
    choice1 = "" 
    choice2 = "" 
    choice3 = "" 
    while(data != 3): 
     key = raw_input("What will this world have?: ") 
     data += 1 
     if (key == "grass"): 
       choice1 = "The world is covered in green grass." 
     elif (key == "water"): 
       choice2 = "The world is covered in water." 
     elif (key == "sky"): 
       choice3 = "The sky is vast and beautiful." 
     if (data >= 3): 
      print("Before you is " + name) 
      print(choice1) 
      print(choice2) 
      print(choice3) 
      raw_input("Press Enter to continue...") 
     else: 
      print("Invalid Option") 


generator() 

Answer 1

這個問題是因爲你在1開始data。 用戶，然後進入他們的第一選擇，而你增加data爲2 用戶接着輸入錫爾第二個選擇，你，你增加data到3

因爲data現在3，它執行你的if data >= 3聲明， 和僅打印choice1和choice2，因爲用戶還沒有給出他們的第三選擇。

如果你設置：

data = 0 

在開始，而不是：

data = 1 

然後用戶必須輸入他們的第三個選擇，你希望它會工作。

更新 要停止打印invalid choice一切的時候，你需要從這裏移動你的其他的位置：

if (data >= 3): 
     print("Before you is " + name) 
     print(choice1) 
     print(choice2) 
     print(choice3) 
     raw_input("Press Enter to continue...") 
    else: 
     print("Invalid Option") 

到這裏：

if (key == "grass"): 
     choice1 = "The world is covered in green grass." 
    elif (key == "water"): 
     choice2 = "The world is covered in water." 
    elif (key == "sky"): 
     choice3 = "The sky is vast and beautiful." 
    else: 
     print("Invalid Option") 

，否則會打印Invalid Option每次循環執行和data < 3。

此外，如果您選擇一個無效的選項，它會弄亂你的data計數器。我建議把一個遞增data行：

while(data != 3): 
    key = raw_input("What will this world have?: ") 
    if (key == "grass"): 
     choice1 = "The world is covered in green grass." 
    elif (key == "water"): 
     choice2 = "The world is covered in water." 
    elif (key == "sky"): 
     choice3 = "The sky is vast and beautiful." 
    else: 
     print("Invalid Option") 
     continue # this will skip the rest of the loop if the option is invalid 

    data += 1 # only increment if the option in valid 
    if (data >= 3): 
     print("Before you is " + name) 
     print(choice1) 
     print(choice2) 
     print(choice3) 
     raw_input("Press Enter to continue...")