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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 _new_theme_part(cls, package):
 """ Create and return a default theme part suitable for use with a notes master. """

        partname = package.next_partname('/ppt/theme/theme%d.xml')
        content_type = CT.OFC_THEME
        theme = CT_OfficeStyleSheet.new_default()
        return XmlPart(partname, content_type, theme, package)