def str_line(lin):
    """
    Returns a string in the form 'marker' + 'linestyle' from a 
    matplotlib.lines.line2D object

    Parameters
    ----------

    lin : matplotlib.lines.line2D object

    Returns
    ----------
    strlin: str
        string in the form 'marker' + 'linestyle'
    """
    strlin = ''
    if lin.get_marker() is not 'None':
        strlin = strlin + lin.get_marker()
    if lin.get_linestyle() is not 'None':
        strlin = strlin + lin.get_linestyle()
    return strlin
