[English]
I created python similar accesing list or string with php substr & strrev functions.

Use: str($string,$pattern)

About the python pattern,
http://docs.python.org/release/1.5.1p1/tut/strings.html
http://effbot.org/zone/python-list.htm

About of pattern structures
[start:stop:step]

Example,
<?php
$s = "fatihmertdogancan";
echo str($s,"1:9:-2");
echo "<br/>";
echo str($s,"1:-3:-2");
echo "<br/>";
echo str($s,"1:-11:-5");
echo "<br/>";
echo str($s,"1:9:4");
?>

Output,
thetoacn
eht
aom
htan

This is function phpfiddle link: http://phpfiddle.org/main/code/e82-y5d

or source;

<?php
    function str($str,$pattern){
        //[start:stop:step]
        //pattern ->            ([-]?[0-9]*|\s):([-]?[0-9]*|\s):([-]?[0-9]*|\s)
        preg_match("/([-]?[0-9]*|\s?):([-]?[0-9]*|\s?):?([-]?[0-9]*|\s?)/", $pattern, $yakala);
        $start = $yakala[1];
        $stop = $yakala[2];
        $step = $yakala[3];
        
        if(empty($start) && empty($stop) && $step == "-1"){//istisna durum
            return strrev($str);
        }else if(empty($start) && empty($stop) && isset($step)){//istisna durum
            $rev = "";
            $yeni = "";
            if($step[0] == "-" && $stop != "-1"){$rev = "VAR";}
            $atla = abs($step);
            for($i = 0; $i <= strlen($str); $i++){
                $offset = $i*$atla;
                if(isset($str[$offset])){
                    $yeni = $yeni.$str[$offset];
                }
            }
            if($rev != "VAR"){
                return substr($yeni,0,strlen($str)-1);
                //"hepsi boş, step dolu o da +";
            }else{
                return strrev(substr($yeni,0,strlen($str)-1));
                //"hepsi boş, step dolu o da -";
            }
        }
        
        if(empty($start) && empty($stop) && empty($step)){
            return $str;
            //"hepsi boş";
        }else if(empty($start)){
            if(isset($stop) && empty($step)){
                $rev = "";
                if($stop[0] == "-"){$rev = "VAR";}
                if($rev != "VAR"){
                    return substr($str,0,$stop);
                    //"start ve step boş, stop dolu"
                }else{
                    return strrev(substr($str,0,$stop));
                    //"start ve step boş, stop -1";
                }
            }else if(isset($stop) && isset($step)){
                $rev = "";
                if($stop[0] == "-"){$rev = "VAR";}
                $yeni = "";
                if($step == 1){
                    if($rev != "VAR"){
                        return $str;
                        //"start boş, stop ve step dolu, step 1";
                    }else{
                        return strrev(substr($str,0,abs($stop))); //abs -> mutlak değer (-5 = 5)
                        //"start boş, stop -, step dolu, step 1";
                    }
                }else{
                    $atla = abs($step);
                    for($i = 0; $i <= strlen($str); $i++){
                        $offset = $i*$atla;
                        if(isset($str[$offset])){
                            $yeni = $yeni.$str[$offset];
                        }
                    }
                    if($rev != "VAR"){
                        return substr($yeni,0,$stop);
                        //"start boş, step ve stop dolu";
                    }else{
                        return strrev(substr($yeni,0,abs($stop)));
                        //"start boş, step ve stop -";
                    }
                }
            }
        //start boş değilse
        }else if(!empty($start)){
            if(isset($stop) && empty($step)){
                $rev = "";
                if($stop[0] == "-"){$rev = "VAR";}
                if($rev != "VAR"){
                    return substr($str,$start,$stop);
                    //return "step boş, start ve stop dolu";
                }else{
                    return strrev(substr($str,0,abs($stop)));
                    //"step boş, start ve stop dolu, stop -";
                }
            }else if(isset($stop) && isset($step)){
                
                //hepsi dolu
                $rev = "";
                if($stop[0] == "-"){$rev = "VAR";}
                $yeni = "";
                if($step == 1){
                    if($rev != "VAR"){
                        return substr($str,$start,$stop);
                        //"hepsi dolu, step 1";
                    }else{
                        return substr($str,$start,abs($stop));
                        //"hepsi dolu, step 1, stop -";
                    }
                }else{
                    if($stop[0] == "-"){$rev = "VAR";}
                    $atla = abs($step);
                    for($i = 0; $i <= strlen($str); $i++){
                        $offset = $i*$atla;
                        if(isset($str[$offset])){
                            $yeni = $yeni.$str[$offset];
                        }
                    }
                    if($rev != "VAR"){
                        return substr($yeni,$start,$stop);
                        //"hepsi dolu";
                    }else{
                        return strrev(substr($yeni,$start,abs($stop)));
                        //"hepsi dolu, stop -";
                    }
                }
            }
        }
    }
?>

Good works..