在while循环中分配后只有两个变量

Question

当我运行代码时，它要求用户输入3次，但是当条件满足时，它仍然只打印其中的2个。为什么？我对Python很陌生，但在谷歌上看到任何答案都很疯狂，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

这个问题是因为你在1开始data。 用户，然后进入他们的第一选择，而你增加data为2 用户接着输入锡尔第二个选择，你，你增加data到3

因为data现在3，它执行你的if data >= 3声明， 和仅打印choice1和choice2，因为用户还没有给出他们的第三选择。

如果你设置：

data = 0 

在开始，而不是：

data = 1 

然后用户必须输入他们的第三个选择，你希望它会工作。

更新 要停止打印invalid choice一切的时候，你需要从这里移动你的其他的位置：

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

到这里：

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") 

，否则会打印Invalid Option每次循环执行和data < 3。

此外，如果您选择一个无效的选项，它会弄乱你的data计数器。我建议把一个递增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...")