String equivalents

string_equivalents.php

// Python equivalent:
// string[start:end]
function tt_str_slice($string, $start=NULL, $end=NULL) {
    $length = strlen($string);

    if ($start === NULL) {
        $start = 0;
    } else if ($start < 0) {
        $start = $length + $start;
        if ($start < 0) {
            $start = 0;
        }
    }

    if ($end === NULL) {
        $end = $length;
    } else if ($end < 0) {
        $end = $length + $end;
        if ($end > $length) {
            $end = $length;
        }
    }

    if ($end <= $start) {
        return '';
    }

    return substr($string, $start, $end - $start);
}

// Python equivalent:
// string.startswith(value)
function tt_str_startswith($string, $value) {
    if ($value === '') {
        return TRUE;
    }
    return tt_str_slice($string, 0, strlen($value)) === $value;
}

// Python equivalent:
// string.endswith(value)
function tt_str_endswith($string, $value) {
    if ($value === '') {
        return TRUE;
    }
    return tt_str_slice($string, -strlen($value)) === $value;
}