Check for palindrome

Question

This is a question from one exam. Lets say we have a function, def palindrome (s), and we call it. If it is a palindrome, the function should return True.

def palindrome(s):
    ...
palindrome("radar")

In order to check if it is a palindrome, i tried to reverse the string in order to see if it was the same. I used s.find(s[::-1]).

The alternatives from the exam was:

return  bool(s.find(s[::-1]))
return  not(bool(s.find(s[::-1]

I don't understand the difference between these two alternatives, can someone explain?

Possible duplicate of [How to check for palindrome using Python logic](https://stackoverflow.com/questions/17331290/how-to-check-for-palindrome-using-python-logic) — Ardweaden, Jul 24 '19 at 13:26

score 1 · Answer 1 · answered Jul 24 '19 at 13:57

The equality operator '==' returns True or False

def palindrome(s):
    reverse_str = s[::-1]
    return s == reverse_str

palindrome("radar")

True

The find() method finds the first occurrence of the specified value or returns -1 if the value is not found.

def palindrome(s):
    reverse_str = s[::-1]
    return s.find(reverse_str)

palindrome("radar")

0

score 0 · Answer 2 · answered Jul 24 '19 at 13:37

Solution #1

return  bool(s.find(s[::-1]))

This is just the same as your solution. The only difference is it gets casted to a boolean type.

The bool() method converts a value to Boolean (True or False) using the standard truth testing procedure.

Solution #2

return  not(bool(s.find(s[::-1]))

Just the same as previous solution but the result gets flipped. Why flip it? When found the result will be 0, when not found the result will be -1. This results in False (0) and True(-1). So it's weird that when found it gives False and when not found it gives True. That's why it's flipped.

Check for palindrome

2 Answers2

Solution #1

Solution #2