Parameters
    ----------
    stroke_id_needle : int
        Identifier for the stroke of which the symbol should get found.
    segmentation : list of lists of integers
        An ordered segmentation of strokes to symbols.

    Returns
    -------
    The symbol index in which stroke_id_needle occurs

    Examples
    --------
    >>> _get_symbol_index(3, [[0, 1, 2], [3, 4, 5], [6, 7]])
    1
    >>> _get_symbol_index(6, [[0, 1, 2], [3, 4, 5], [6, 7]])
    2
    >>> _get_symbol_index(7, [[0, 1, 2], [3, 4, 5], [6, 7]])
    2

def _get_symbol_index(stroke_id_needle, segmentation):
    """
    Parameters
    ----------
    stroke_id_needle : int
        Identifier for the stroke of which the symbol should get found.
    segmentation : list of lists of integers
        An ordered segmentation of strokes to symbols.

    Returns
    -------
    The symbol index in which stroke_id_needle occurs

    Examples
    --------
    >>> _get_symbol_index(3, [[0, 1, 2], [3, 4, 5], [6, 7]])
    1
    >>> _get_symbol_index(6, [[0, 1, 2], [3, 4, 5], [6, 7]])
    2
    >>> _get_symbol_index(7, [[0, 1, 2], [3, 4, 5], [6, 7]])
    2
    """
    for symbol_index, symbol in enumerate(segmentation):
        if stroke_id_needle in symbol:
            return symbol_index
    return None