def append(self, header, f, _left=False):
        """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.

        """
        self.items_length += len(header)
        if _left:
            self.deque.appendleft((header, f))
        else:
            self.deque.append((header, f))
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.