pandas-dev/pandas · error · ValueError

Passing in 'timedelta' dtype with no precision is not…

Error message

Passing in 'timedelta' dtype with no precision is not allowed. Please pass in 'timedelta64[ns]' instead.

What it means

Raised by _validate_td64_dtype when the supplied dtype is the unit-less `timedelta64` (numpy dtype 'm8', no precision). Pandas requires an explicit resolution (GH#24806); a bare timedelta dtype is ambiguous because the backing nanosecond representation needs a defined unit. The message directs the caller to use 'timedelta64[ns]'.

Solutions

1. Specify a resolution: use 'timedelta64[ns]' (or 's','ms','us' as supported).
2. Omit the dtype entirely and let pandas infer it from timedelta data.
3. Validate dtype strings before passing them to constructors.

Example fix

# before
pd.Index(pd.to_timedelta([1, 2], unit='D'), dtype='timedelta')  # ValueError

# after
pd.Index(pd.to_timedelta([1, 2], unit='D'), dtype='timedelta64[ns]')

import numpy as np

def validate_td_dtype_str(dtype_str: str) -> bool:
    try:
        dt = np.dtype(dtype_str)
    except TypeError:
        return False
    return dt != np.dtype('m8') and dt.kind == 'm'

null

try:
    idx = pd.TimedeltaIndex(data, dtype=dtype)
except ValueError as e:
    if 'no precision' in str(e):
        idx = pd.TimedeltaIndex(data, dtype='timedelta64[ns]')
    else:
        raise

When it happens

Trigger: Constructing a TimedeltaIndex/Index with dtype='timedelta' or dtype='timedelta64' (no unit), e.g. `pd.Index([], dtype='timedelta')`.

Common situations: Copying a loose dtype string from documentation or older code; building dtype dynamically without appending a unit.

Related errors

• dtype ' ' is invalid, should be np.timedelta64 dtype
• Supported timedelta64 resolutions are 's', 'ms', 'us', 'ns'
• Cannot convert input with unit
• Cannot divide vectors with unequal lengths
• Cannot multiply with

AI-assisted analysis of pandas-dev/pandas@3b7651241d (2026-08-11). Data as JSON: /api/errors/645da3b018f50624. Report an issue: GitHub.

Appendix: source

Thrown at pandas/core/arrays/timedeltas.py:1433

    errors to be ignored; they are caught and subsequently ignored at a
    higher level.
    """
    # coerce Index to np.ndarray, converting string-dtype if necessary
    values = np.asarray(data, dtype=np.object_)

    result = array_to_timedelta64(values, unit=unit, errors=errors)
    return result


def _validate_td64_dtype(dtype) -> DtypeObj:
    dtype = pandas_dtype(dtype)
    if dtype == np.dtype("m8"):
        # no precision disallowed GH#24806
        msg = (
            "Passing in 'timedelta' dtype with no precision is not allowed. "
            "Please pass in 'timedelta64[ns]' instead."
        )
        raise ValueError(msg)

    if not lib.is_np_dtype(dtype, "m"):
        raise ValueError(f"dtype '{dtype}' is invalid, should be np.timedelta64 dtype")
    elif not is_supported_dtype(dtype):
        raise ValueError("Supported timedelta64 resolutions are 's', 'ms', 'us', 'ns'")

    return dtype

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