code: def append_column(self, data_array, ckey='temp'):
          
          if not type(ckey) is str:
              print("ERROR: ckey should be a string!")
              return
  
          if ckey in self.ckeys:
              print("ERROR: ckey '"+ckey+"' already exists!")
              return
  
          return self.insert_column(data_array, ckey)
docs: This will append a new column and fill it with the data from the
          the supplied array.
          
          Parameters
          ----------
          data_array  
              Data; can be a list, but will be converted to numpy array
          ckey        
              Name of the column.