$re = '/\w+(?=\()|\b[xy]\b/';
$str = 'def gcd(x, y):
"""Sample docstring."""
if x == y:
return x
if x > y:
if y == 0: return x
return gcd(x-y, y)
if y > x:
if x == 0: return y
# Sample comment.
return gcd(x, y-x)';
$subst = "X";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php