code: def _set_font(self, family, size, bold, italic):
          
          def iter_rPrs(txBody):
              for p in txBody.p_lst:
                  for elm in p.content_children:
                      yield elm.get_or_add_rPr()
                  # generate a:endParaRPr for each <a:p> element
                  yield p.get_or_add_endParaRPr()
  
          def set_rPr_font(rPr, name, size, bold, italic):
              f = Font(rPr)
              f.name, f.size, f.bold, f.italic = family, Pt(size), bold, italic
  
          txBody = self._element
          for rPr in iter_rPrs(txBody):
              set_rPr_font(rPr, family, size, bold, italic)
docs: Set the font properties of all the text in this text frame to
          *family*, *size*, *bold*, and *italic*.