code: def _set_marX(self, marX, value):
          
          if value is None and self.tcPr is None:
              return
          tcPr = self.get_or_add_tcPr()
          setattr(tcPr, marX, value)
docs: Set value of marX attribute on ``<a:tcPr>`` child element. If *marX*
          is |None|, the marX attribute is removed. *marX* is a string, one of
          ``('marL', 'marR', 'marT', 'marB')``.