Method _generate_range

pandas/core/arrays/datetimes.py:414–537

(
        cls,
        start,
        end,
        periods: int | None,
        freq,
        tz=None,
        normalize: bool = False,
        ambiguous: TimeAmbiguous = "raise",
        nonexistent: TimeNonexistent = "raise",
        inclusive: IntervalClosedType = "both",
        *,
        unit: TimeUnit = "ns",
    )

    @classmethod
    def _generate_range(
        cls,
        start,
        end,
        periods: int | None,
        freq,
        tz=None,
        normalize: bool = False,
        ambiguous: TimeAmbiguous = "raise",
        nonexistent: TimeNonexistent = "raise",
        inclusive: IntervalClosedType = "both",
        *,
        unit: TimeUnit = "ns",
    ) -> Self:
        periods = dtl.validate_periods(periods)
        if freq is None and any(x is None for x in [periods, start, end]):
            raise ValueError("Must provide freq argument if no data is supplied")

        if com.count_not_none(start, end, periods, freq) != 3:
            raise ValueError(
                "Of the four parameters: start, end, periods, "
                "and freq, exactly three must be specified"
            )
        freq = to_offset(freq)

        if start is not None:
            start = Timestamp(start)

        if end is not None:
            end = Timestamp(end)

        if start is NaT or end is NaT:
            raise ValueError("Neither `start` nor `end` can be NaT")

        if unit is not None:
            if unit not in ["s", "ms", "us", "ns"]:
                raise ValueError("'unit' must be one of 's', 'ms', 'us', 'ns'")
        else:
            unit = "ns"

        if start is not None:
            start = start.as_unit(unit, round_ok=False)
        if end is not None:
            end = end.as_unit(unit, round_ok=False)

        left_inclusive, right_inclusive = validate_inclusive(inclusive)
        start, end = _maybe_normalize_endpoints(start, end, normalize)
        tz = _infer_tz_from_endpoints(start, end, tz)

        if tz is not None:
            # Localize the start and end arguments
            start = _maybe_localize_point(start, freq, tz, ambiguous, nonexistent)
            end = _maybe_localize_point(end, freq, tz, ambiguous, nonexistent)

        if freq is not None:
            # Offset handling:
            # Ticks (fixed-duration like hours/minutes): keep tz; do absolute-time math.
            # Other calendar offsets: drop tz; do naive wall time; localize once later