'Return the id of the style corresponding to *style_or_name*, or
|None| if *style_or_name* is |None|. If *style_or_name* is not
a style object, the style is looked up using *style_or_name* as
a style name, raising |ValueError| if no style with that name is
defined. Raises |ValueError| if the target style is not of
*style_type*.'

def get_style_id(self, style_or_name, style_type):

    if (style_or_name is None):
        return None
    elif isinstance(style_or_name, BaseStyle):
        return self._get_style_id_from_style(style_or_name, style_type)
    else:
        return self._get_style_id_from_name(style_or_name, style_type)
