docs: def set_col_first(df, col_names):
          """set selected columns first in a pandas.DataFrame.
  
          This function sets cols with names given in  col_names (a list) first in
          the DataFrame. The last col in col_name will come first (processed last)
          """
  
          column_headings = df.columns
          column_headings = column_headings.tolist()
          try:
              for col_name in col_names:
                  i = column_headings.index(col_name)
                  column_headings.pop(column_headings.index(col_name))
                  column_headings.insert(0, col_name)
  
          finally:
              df = df.reindex(columns=column_headings)
              return df