pandas-dev/pandas · error · TypeError

ExtensionArray.fillna does not support filling with a dict.

Error message

ExtensionArray.fillna does not support filling with a dict. Use Series.fillna instead.

What it means

Raised as a TypeError by `IntervalArray.fillna` when `value` is a dict. Dict-based filling (per-label) is a Series-level concept and is not implemented on the bare ExtensionArray. Fires at pandas/core/arrays/interval.py:899.

Source

Thrown at pandas/core/arrays/interval.py:899

            values for each index. The value should not be a list. The
            value(s) passed should be either Interval objects or NA/NaN.
        limit : int, default None
            (Not implemented yet for IntervalArray)
            The maximum number of entries where NA values will be filled.
        copy : bool, default True
            Whether to make a copy of the data before filling. If False, then
            the original should be modified and no new memory should be allocated.
            For ExtensionArray subclasses that cannot do this, it is at the
            author's discretion whether to ignore "copy=False" or to raise.

        Returns
        -------
        filled : IntervalArray with NA/NaN filled
        """
        if copy is False:
            raise NotImplementedError
        if isinstance(value, dict):
            raise TypeError(
                "ExtensionArray.fillna does not support filling with a dict. "
                "Use Series.fillna instead."
            )
        if limit is not None:
            raise ValueError("limit must be None")

        value_left, value_right = self._validate_setitem_value(value)

        left = self.left.fillna(value=value_left)
        right = self.right.fillna(value=value_right)
        return self._shallow_copy(left, right)

    def astype(self, dtype, copy: bool = True):
        """
        Cast to an ExtensionArray or NumPy array with dtype 'dtype'.

        Parameters
        ----------

View on GitHub (pinned to 71959b8cb9)

Solutions

1. Call fillna on the Series: `s.fillna({...})`.
2. If working on the array, fill with a single scalar Interval: `ia.fillna(pd.Interval(0,1))`.
3. Map positions manually: build new left/right arrays and reconstruct the IntervalArray.

Example fix

// before
ia.fillna({0: pd.Interval(0, 1)})
// after
pd.Series(ia).fillna({0: pd.Interval(0, 1)}).values

def fillna_interval(ia, value):
    import pandas as pd
    if isinstance(value, dict):
        return pd.Series(ia).fillna(value).values
    return ia.fillna(value)

def is_dict_value(value) -> bool:
    return isinstance(value, dict)

try:
    out = ia.fillna(value)
except TypeError as e:
    if "does not support filling with a dict" in str(e):
        out = pd.Series(ia).fillna(value).values
    else:
        raise

When it happens

Trigger: `ia.fillna({0: pd.Interval(0,1)})`, or calling `.fillna` on the `.values` of a Series with a dict.

Common situations: Calling `.values.fillna({...})` instead of the Series method; copy-pasting a Series fillna pattern onto the array.

Related errors

• limit must be None
• ExtensionArray.fillna does not support filling with a dict.
• cannot diff {type(arr).__name__} on axis={axis}
• {type(arr).__name__} has no 'diff' method. Convert to a suit
• cannot perform both aggregation and transformation operation

AI-assisted analysis of pandas-dev/pandas@71959b8cb9 (2026-08-07). Data as JSON: /api/errors/a2937b138f76ab13. Report an issue: GitHub.