python - 您如何根据给定的用户输入让程序再次运行？

Question

我为一个简单的猜谜游戏制作了这段代码，其中包括输入一个猜数字的输入(由变量 guess_number 定义)。我希望它做的是在输入不正确时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，但我不太了解它(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，你有一个 do-while 语句来完成这个任务，即你可以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。在 Python 中没有这样的语句。但是没关系，您还有其他几种方法可以使代码工作。
所有这些可能性(变体 2 除外!)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 .更强大的是采用用户根本无法输入的数字，例如无穷大:import math; guessing_games = math.inf .
现在所有条件都可以使用 while 循环。顾名思义，它是关于一遍又一遍地执行同一个块。为了防止程序无限运行，我们需要一个终止条件。这在您的情况下很清楚:当用户猜到正确的数字时，块的执行应该停止。
这意味着块应该在 while 循环中运行，直到不再满足循环的条件:while guessing_games != guess_number .当然重要的是变量guessing_games可以在块内更改。这是因为在块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:在块中使用显式终止条件 break陈述

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 向您展示了避免初始化 guessing_games 的可能性。使用 while True (否则如变体 1 和 3 所示，必须进行初始化以避免错误: NameError: name 'guessing_games' is not defined )。但是你必须小心，循环肯定会在某个时候结束。
变体 3:与变体 1 非常相似，不同之处在于成功消息可以看作是 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!")

另见 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一个数字:

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