Function _lazily_encode_cf_datetime

xarray/coding/times.py:1204–1240

(
    dates: T_ChunkedArray,
    units: str | None = None,
    calendar: str | None = None,
    dtype: np.dtype | None = None,
)

def _lazily_encode_cf_datetime(
    dates: T_ChunkedArray,
    units: str | None = None,
    calendar: str | None = None,
    dtype: np.dtype | None = None,
) -> tuple[T_ChunkedArray, str, str]:
    if calendar is None:
        # This will only trigger minor compute if dates is an object dtype array.
        calendar = infer_calendar_name(dates)

    if units is None and dtype is None:
        if dates.dtype == "O":
            units = "microseconds since 1970-01-01"
            dtype = np.dtype("int64")
        else:
            netcdf_unit = _numpy_dtype_to_netcdf_timeunit(dates.dtype)
            units = f"{netcdf_unit} since 1970-01-01"
            dtype = np.dtype("int64")

    if units is None or dtype is None:
        raise ValueError(
            f"When encoding chunked arrays of datetime values, both the units "
            f"and dtype must be prescribed or both must be unprescribed. "
            f"Prescribing only one or the other is not currently supported. "
            f"Got a units encoding of {units} and a dtype encoding of {dtype}."
        )

    chunkmanager = get_chunked_array_type(dates)
    num = chunkmanager.map_blocks(
        _encode_cf_datetime_within_map_blocks,
        dates,
        units,
        calendar,
        dtype,
        dtype=dtype,
    )
    return num, units, calendar


def encode_cf_timedelta(