python - 如何让程序根据给定的用户输入再次运行？

Question

我为一个简单的猜谜游戏编写了这段代码，其中涉及输入一个输入来猜测数字(由变量guess_number 定义)。我想要它做的是，如果输入不正确，则再次运行，并在答案正确时停止//终止，但我无法得到它。我假设我需要一个 while 循环，但我不太理解它(一周前开始编程)。这是基本程序:

guess_number = 33

guessing_games = int(input('Try to guess the number I am thinking of, 1-50: '))

if guessing_games == guess_number:
    print("Great job! You got the number correct!")
elif guessing_games > guess_number:
    print("Too high! Guess again.")
elif guessing_games < guess_number:
    print("Too low! Guess again.")

Answer 1

在其他编程语言中，您可以使用 do-while 语句来完成此任务，即您可以首先向用户询问一个数字，然后执行代码，直到用户给出正确的数字。 Python中没有这样的声明。不过没关系，您还有其他几种方法可以使代码正常工作。

所有这些可能性(除了变体 2!)的共同点是您已经需要初始化一个值来检查 while 循环中的条件。对于您的示例(用户显然可以输入 1 到 50 之间的数字)，只需选择 0 就足够了，例如guessing_games = 0。更稳健的方法是采用用户根本无法输入的数字，例如无穷大:导入数学； guessing_games = math.inf.

现在所有条件都给出使用 while 循环。顾名思义，它是一遍又一遍地执行同一个 block 。为了防止程序无限运行，我们需要一个终止条件。在您的情况下这一点很明显:当用户猜到正确的数字时， block 的执行应该停止。

这意味着该 block 应在 while 循环内运行，直到不再满足循环条件:whileguessing_games !=guess_number。当然，变量 guessing_games 可以在 block 内更改，这一点很重要。出现这种情况是因为在 block 执行开始时总是要求用户输入新数字。

变体 1:使用简单的终止条件并在 while 循环后打印成功消息

import math

guess_number = 33
guessing_games = math.inf

while guessing_games != guess_number:
    guessing_games = int(input("Try to guess the number I am thinking of, 1-50: "))

    if guessing_games > guess_number:
        print("Too high! Guess again.")
    elif guessing_games < guess_number:
        print("Too low! Guess again.")

print("Great job! You got the number correct!")

变体 2:通过 break 语句在 block 内使用显式终止条件

guess_number = 33

while True:
    guessing_games = int(input("Try to guess the number I am thinking of, 1-50: "))

    if guessing_games > guess_number:
        print("Too high! Guess again.")
    elif guessing_games < guess_number:
        print("Too low! Guess again.")
    else:
        print("Great job! You got the number correct!")
        break

变体 2 向您展示了使用 while True 避免初始化 guessing_games 的可能性(否则如变体 1 和 3 所示，必须进行初始化以避免错误:NameError:名称“guessing_games”未定义)。但你必须小心，循环肯定会在某个时刻结束。

变体 3:与变体 1 非常相似，不同之处在于成功消息可以被视为 while 循环的一部分。

import math

guess_number = 33
guessing_games = math.inf

while guessing_games != guess_number:
    guessing_games = int(input("Try to guess the number I am thinking of, 1-50: "))

    if guessing_games > guess_number:
        print("Too high! Guess again.")
    elif guessing_games < guess_number:
        print("Too low! Guess again.")
else:
    print("Great job! You got the number correct!")

另请参阅Python documentation :

The while statement is used for repeated execution as long as an expression is true:

while_stmt ::=  "while" assignment_expression ":" suite
                ["else" ":" suite]

This repeatedly tests the expression and, if it is true, executes the first suite; if the expression is false (which may be the first time it is tested) the suite of the else clause, if present, is executed and the loop terminates.

A break statement executed in the first suite terminates the loop without executing the else clause’s suite. A continue statement executed in the first suite skips the rest of the suite and goes back to testing the expression.

我实际上建议的最后一件事是检查用户是否输入了数字:

try:
    guessing_games = int(input("Try to guess the number I am thinking of, 1-50: "))
except ValueError:
    print("Only numbers are allowed.")
    continue