Three Reliable Ways to Detect Palindromes in Python

In a Python discussion group a user asked how to correctly determine whether a positive integer is a palindrome. The original code attempted the check but placed the result output in the wrong location.

1. Original Code

x=input("请输入一个正整数：")
long=len(x)
end=str(x[long-1])
end=int(end)
x=int(x)

if x<0 or end ==0:
    print("不是回文数")
else:
    x=str(x)
    for i in range(len(x)):
        if x[i]==x[long-i-1]:
            continue
        else:
            print("不是回文数")
            break
    print("是回文数")

2. Solution 1 – Using for‑else

Placing the success message inside the else clause of the for loop ensures it runs only when the loop completes without breaking.

x=input("请输入一个正整数：")
long=len(x)
end=str(x[long-1])
end=int(end)
x=int(x)

if x<0 or end ==0:
    print("不是回文数")
else:
    x=str(x)
    for i in range(len(x)):
        if x[i]==x[long-i-1]:
            continue
        else:
            print("不是回文数")
            break
    else:
        print("是回文数")

3. Solution 2 – Using all()

d = ['12321', '123', '1221', '1212']
for s in d:
    l = len(s)
    if all(s[i] == s[l-i-1] for i in range(l)):
        print(f'{s}是回文数')
    else:
        print(f'{s}不是回文数')

4. Solution 3 – Using Slice Reversal

d = ['12321', '123', '1221', '1212']
for s in d:
    if s == s[::-1]:
        print(f'{s}是回文数')
    else:
        print(f'{s}不是回文数')

5. Why for‑else Works

The else block attached to a for loop executes only when the loop finishes normally, i.e., without encountering a break. This makes it ideal for signalling that all characters matched and the number is a palindrome.

Conclusion

The three approaches above reliably solve the palindrome‑checking problem, each illustrating a different Python technique—loop control with for‑else, collective condition checking with all(), and concise slicing.