[Python] Palindromes and string slicing. Performance

There are a lot of ways to check if string is a palindrome. Plenty of them listed here

This question is not about "how" but rather about performance.

I was assuing that is_palindrome should be twice faster than is_palindrome0 because it does len/2 iterations in the worst case.

However, in reality, is_palindrome takes more than 30 seconds to check all the strings while is_palindrome0 gets the job done in less than half of a second!

Test-case

def is_palindrome(s):
for i in range(len(s) // 2):
if s != s[len(s)-i-1]:
return 0
return 1

def is_palindrome0(s):
if s == s[::-1]:
return 1
else:
return 0

N = 500
L = 99999

sss = '101' * L

import time

start = time.time()
print(sum([1 for i in range(N) if is_palindrome0(sss+sss[i:])]))
end = time.time()
print(f'{(end - start):.2f}')

start = time.time()
print(sum([1 for i in range(N) if is_palindrome(sss+sss[i:])]))
end = time.time()
print(f'{(end - start):.2f}')


Output

168
0.40
168
34.20


Any ideas why string slicing is so crazy fast? How to debug further?

Apologies if I missed answered question with in-depth performance comparison.

UPDATE. Taking into account Frank's comment.

def is_palindrome(s):
l = len(s)
for i in range(l // 2):
if s != s[l-i-1]:
return 0
return 1

def is_palindrome0(s):
if s == s[::-1]:
return 1
else:
return 0

N = 500
L = 99999

sss = '101' * L

import time

start = time.time()
print(sum([1 for i in range(N) if is_palindrome0(sss+sss[i:])]))
end = time.time()
print(f'{(end - start):.2f}')

start = time.time()
print(sum([1 for i in range(N) if is_palindrome(sss+sss[i:])]))
end = time.time()
print(f'{(end - start):.2f}')


A bit faster but still around 50x times slower.

168
0.41
168
25.11

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