Python中用while和if实现回文检查器的无限循环问题

Let's break down why your code is stuck in an infinite loop first, then fix it to work exactly as you want.

The Problem with Your Current Code #

Your approach has two critical issues causing the endless "sorry try again" messages:

• No fresh input after the first attempt: You only capture the user's input once, before calling the function. If it's not a palindrome, the loop keeps rechecking that same non-palindromic string over and over.
• Loop condition never exits for non-palindromes: When the input fails the check, you set b = 1—since 1%2 != 0 is still true, the loop immediately runs again, creating an infinite cycle.

The Fixed Code #

We need to restructure the logic to keep asking for input until the user enters a valid palindrome. Here's a clean, working version:

def palindrome_check():
    while True:
        user_input = str(input('enter a valid string: '))
        if user_input == user_input[::-1]:
            print('its a palindrome')
            break  # Exit the loop once we get a valid palindrome
        else:
            print('sorry try again ')

palindrome_check()

What Changed? #

• Input moved inside the loop: Now every time the user enters a non-palindrome, the loop prompts for a brand new string instead of rechecking the old one.
• Simplified loop structure: Using while True creates a straightforward infinite loop that we only exit with break when the palindrome condition is met—no need for a dummy variable like b.
• Removed redundant return value: Since the function's purpose is to validate input until success, returning the input isn't necessary (but you can add it back if you need to use the valid string later).

Optional: Case-Insensitive Check #

If you want the checker to ignore uppercase/lowercase differences (e.g., "Racecar" should count as a palindrome), adjust the condition to:

if user_input.lower() == user_input.lower()[::-1]:

内容的提问来源于stack exchange，提问作者Siddharth Chandran