CODEWITHSUNDEEP
python
Apollo
Apollo

Reputation: 9054

Determining if string is palindrome

I wrote two simple functions to determine if a string is a palindrome. I thought they were equivalent, but 2 doesn't work. Why is this?

1

def is_palindrome(string):
    if string == string[::-1]:
        return True
    else:
        return False

2

def is_palindrome(string):
    if string == reversed(string):
        return True
    else:
        return False

Upvotes: 6

Views: 370

Answers (4)

Shubhayan Chakrabarty
Shubhayan Chakrabarty

Reputation: 1

str = input("Enter a string")
print("\n".join(["Inserted string is" + "NOT"*((str[::-1])!=str)+ " a palindrome"]))

Upvotes: 0

pylang
pylang

Reputation: 44475

For strings:

def is_palindrome(s):
    """Return True if a string is a palindrome."""
    return s == s[::-1]

For general iterables (including strings):

def is_palindrome(iterable):
    """Return True if an iterable is a palindrome."""
    if list(iteable) == list(reversed(iterable))

Upvotes: 0

Alex Martelli
Alex Martelli

Reputation: 881575

In the second one, you need to make a str from the reversed type instance -- it's not hard:

if string == ''.join(reversed(string)):

Upvotes: 1

Simeon Visser
Simeon Visser

Reputation: 122336

reversed doesn't create a string but a 'reversed' object:

>>> reversed('radar')
<reversed object at 0x1102f99d0>

As such, the string 'radar' does not compare equal to the object reversed('radar'). To make it work, you need to make sure the reversed object is actually evaluated:

def is_palindrome(string):
    if string == u''.join(reversed(string)):
        return True
    else:
        return False

The u''.join(reversed(string)) inserts u'' in between each of the characters in the string and this leads to the reversed string being turned into a string object.

Upvotes: 10

Related Questions