求助：Python回文判断代码异常，输入'race'误判为TRUE

Hey there! Let's dig into why your code is giving the wrong result for inputs like "race".

The Root Problem #

Your current logic has a critical flaw: every time it finds a matching pair of characters, it overwrites the b variable to "TRUE"—even if it already found a mismatch earlier. For "race", here's what happens step by step:

1. First loop iteration: compares 'r' (index 0) with 'e' (index 3) → mismatch, so b = "FALSE"
2. Second iteration: compares 'r' (index 0) with 'c' (index 2) → mismatch, b stays "FALSE"
3. Third iteration: compares 'r' (index 0) with 'a' (index 1) → mismatch, b stays "FALSE"
4. Fourth iteration: compares 'r' (index 0) with 'r' (index 0) → match, so b gets set to "TRUE"

That final match overwrites the correct "FALSE" result, which is why you're seeing the wrong output.

Fixed Version of Your Original Code #

We can fix this by:

• Starting with a default assumption that the string is a palindrome
• Immediately marking it as not a palindrome and stopping the loop as soon as a mismatch is found
• Only comparing the first half of the string to the second half (no need to check every character twice)

string = input("Please enter any word: ")
a = 0
string_length = len(string)
is_palindrome = True  # Start with the assumption it's a palindrome

# Only loop through the first half of the string
for string_index in range(string_length - 1, string_length // 2 - 1, -1):
    character = string[string_index]
    if string[a] != character:
        is_palindrome = False
        break  # No need to check further once a mismatch is found
    a += 1

print("TRUE" if is_palindrome else "FALSE")

A More Pythonic Approach #

If you want a simpler solution, Python lets you reverse a string in one line with slicing. This is clean and efficient:

string = input("Please enter any word: ")
is_palindrome = string == string[::-1]
print("TRUE" if is_palindrome else "FALSE")

Here, string[::-1] creates a reversed copy of the original string. We just compare the two—if they're identical, it's a palindrome!

内容的提问来源于stack exchange，提问作者Mehdi Rizvi