code: def concat(self, *dss, **kwargs):
          
          try:
              df = pd.DataFrame()
              for dsx in dss:
                  df = pd.concat([df, dsx.df], **kwargs)
              self.df = df
          except Exception as e:
              self.err(e, "Can not concatenate data")
docs: Concatenate dataswim instances from and
                  set it to the main dataframe
  
          :param dss: dataswim instances to concatenate
          :type dss: Ds
          :param kwargs: keyword arguments for ``pd.concat``