Method fillna

pandas/core/internals/blocks.py:1314–1345

fillna on the block with the value. If we fail, then convert to block to hold objects instead and try again

(
        self,
        value,
        limit: int | None = None,
        inplace: bool = False,
    )

        return [self.make_block(result)]

    def fillna(
        self,
        value,
        limit: int | None = None,
        inplace: bool = False,
    ) -> list[Block]:
        """
        fillna on the block with the value. If we fail, then convert to
        block to hold objects instead and try again
        """
        # Caller is responsible for validating limit; if int it is strictly positive
        inplace = validate_bool_kwarg(inplace, "inplace")

        if not self._can_hold_na:
            # can short-circuit the isna call
            noop = True
        else:
            mask = isna(self.values)
            mask, noop = validate_putmask(self.values, mask)

        if noop:
            # we can't process the value, but nothing to do
            return [self.copy(deep=False)]

        if limit is not None:
            mask[mask.cumsum(self.values.ndim - 1) > limit] = False

        if inplace:
            nbs = self.putmask(mask.T, value)
        else:
            nbs = self.where(value, ~mask.T)
        return extend_blocks(nbs)

    def pad_or_backfill(
        self,