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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_font_size(document, style):
 """Get font size defined for this style. It will try to get font size from it's parent style if it is not defined by original style. :Args: - document (:class:`ooxml.doc.Document`):
 Document object - style (:class:`ooxml.doc.Style`):
 Style object :Returns: Returns font size as a number. -1 if it can not get font size. """


    font_size = style.get_font_size()

    if  font_size == -1:
        if style.based_on:
            based_on = document.styles.get_by_id(style.based_on)
            if based_on:
                return _get_font_size(document, based_on)

    return font_size