def addJunctionPos(shape, fromPos, toPos):
    """Extends shape with the given positions in case they differ from the
    existing endpoints. assumes that shape and positions have the same dimensionality"""
    result = list(shape)
    if fromPos != shape[0]:
        result = [fromPos] + result
    if toPos != shape[-1]:
        result.append(toPos)
    return result
Extends shape with the given positions in case they differ from the
    existing endpoints. assumes that shape and positions have the same dimensionality