pandas-dev/pandas · error · ValueError

Must provide freq argument if no data is supplied

Error message

Must provide freq argument if no data is supplied

What it means

Raised in _generate_range when freq is None and at least one of start/end/periods is also None. Without freq there is no stride to generate from, so generating a range needs all anchor information; the check fires before the three-of-four counting so it produces a clearer message.

Source

Thrown at pandas/core/arrays/datetimes.py:406

    @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:

View on GitHub (pinned to 71959b8cb9)

Solutions

1. Pass a freq (e.g. freq='D', 'h', to_offset('W-MON')).
2. If you know start+end+periods, supply two of them and let pandas compute freq implicitly is NOT allowed — freq is required when any anchor is missing, so supply it.
3. When building a one-element range, pass periods=1 and freq.

Example fix

# before
pd.date_range(start='2020-01-01')

# after
pd.date_range(start='2020-01-01', periods=5, freq='D')

if freq is None and any(x is None for x in (start, end, periods)):
    raise ValueError('freq required when any of start/end/periods is missing')

try:
    pd.date_range(start=start, end=end, periods=periods, freq=freq)
except ValueError as e:
    if 'Must provide freq' in str(e):
        pd.date_range(start=start, end=end, periods=periods, freq='D')
    else: raise

When it happens

Trigger: pd.date_range(start='2020-01-01', periods=None, freq=None); pd.date_range() with no arguments; pd.date_range(end=...) with neither freq nor periods. Reused parameter dict that left freq unset.

Common situations: Calling date_range with defaults, expecting a daily stride, but freq is keyword-only and defaults to None in _generate_range. Config-driven calls where freq was omitted. Refactor that introduced a None fallback for freq.

Related errors

• Inferred frequency {inferred} from passed values does not co
• periods must be an integer, got {periods}
• Of the four parameters: start, end, periods, and freq, exact
• Neither `start` nor `end` can be NaT
• Must specify a valid frequency: {freq}

AI-assisted analysis of pandas-dev/pandas@71959b8cb9 (2026-08-07). Data as JSON: /api/errors/0a68bb2741d2d115. Report an issue: GitHub.