<s> import datetime <EOL> def big_dt_to_num ( big_dt_col ) : <EOL> return big_dt_col . map ( datetime . datetime . timestamp , na_action = '<STR_LIT:ignore>' ) <EOL> def num_to_big_dt ( num_col ) : <EOL> return num_col . map ( datetime . datetime . fromtimestamp , na_action = '<STR_LIT:ignore>' ) </s>
