def _center(txt, width):
    """
    Return a string of length `width` with the string `txt` centered

    >>> _center('abc', 14)
    '     abc      '
    """
    left = ' ' * int((width - len(txt)) / 2)
    right = ' ' * (width - len(txt) - len(left))
    return '%s%s%s' % (left, txt, right)
