How to find first non-repetitive character from a string?

<?php
    // In an array mapped character to frequency, 
    // find the first character with frequency 1.
    echo array_search(1, array_count_values(str_split('abbcabz')));

Python:

def first_non_repeating(s):
 for i, c in enumerate(s):
  if s.find(c, i+1) < 0:
   return c
 return None

Same in PHP:

function find_first_non_repetitive($s)
{
 for($i = 0; i < strlen($s); i++) {
  if (strpos($s, $s[i], i+1) === FALSE)
   return $s[i];
 }
}