code: def _parse_datetime(sas_datetime: float, unit: str):
      if isna(sas_datetime):
          return pd.NaT
  
      if unit == "s":
          return datetime(1960, 1, 1) + timedelta(seconds=sas_datetime)
  
      elif unit == "d":
          return datetime(1960, 1, 1) + timedelta(days=sas_datetime)
  
      else:
          raise ValueError("unit must be 'd' or 's'")
  
imports: from __future__ import annotations
  from collections import abc
  from datetime import datetime, timedelta
  import sys
  from typing import TYPE_CHECKING
  import numpy
  from pandas._libs.byteswap import read_double_with_byteswap, read_float_with_byteswap, read_uint16_with_byteswap, read_uint32_with_byteswap, read_uint64_with_byteswap
  from pandas._libs.sas import Parser, get_subheader_index
  from pandas._libs.tslibs.conversion import cast_from_unit_vectorized
  from pandas.errors import EmptyDataError
  import pandas
  from pandas import DataFrame, Timestamp, isna
  from pandas.io.common import get_handle
  import pandas.io.sas.sas_constants
  from pandas.io.sas.sasreader import ReaderBase
label_desc: Use image node_id 1 for calling a global function with example usage: _parse_datetime(sas_datetime, unit) and returns: pd, unknown, unknown