code: def append(self, header, f, _left=False):
          
          self.items_length += len(header)
          if _left:
              self.deque.appendleft((header, f))
          else:
              self.deque.append((header, f))
docs: Add a column to the table.
  
          Args:
              header (str):
                  Column header
  
              f (function(datum)->str):
                  Makes the row string from the datum. Str returned by f should
                  have the same width as header.