docs: def weighted_mean_df (df, **kwargs):
      """The same as :func:`weighted_mean`, except the argument is expected to be a
     two-column :class:`pandas.DataFrame` whose first column gives the data
     values and second column gives their uncertainties. Returns
     ``(weighted_mean, uncertainty_in_mean)``.
  
      """
      return weighted_mean (df[df.columns[0]], df[df.columns[1]], **kwargs)