'Append one `Column` to the column definition.'

def add_col(self, column):

    if (not isinstance(column, Column)):
        raise AssertionError
    self._arrays.append(column.array)
    del self.dtype
    del self._recformats
    del self._dims
    del self.names
    del self.formats
    self.columns.append(column)
    column._add_listener(self)
    self._notify('column_added', self, column)
    return self
