'Prepares the given column for insert/append.'

def _clean_col(self, col):

    col = list(col)
    if self.headers:
        header = [col.pop(0)]
    else:
        header = []
    if ((len(col) == 1) and hasattr(col[0], '__call__')):
        col = list(map(col[0], self._data))
    col = tuple((header + col))
    return col
