pandas-dev/pandas · error · KeyError

{key}

Error message

{key}

What it means

Raised by DeepChainMap.__delitem__ when the requested key is not present in any of the chained mappings. DeepChainMap backs the eval/query scope stack, so deleting a name that was never bound (or already removed) surfaces as a bare KeyError whose message is just the key.

Source

Thrown at pandas/core/computation/scope.py:52

    def __setitem__(self, key: _KT, value: _VT) -> None:
        for mapping in self.maps:
            if key in mapping:
                mapping[key] = value
                return
        self.maps[0][key] = value

    def __delitem__(self, key: _KT) -> None:
        """
        Raises
        ------
        KeyError
            If `key` doesn't exist.
        """
        for mapping in self.maps:
            if key in mapping:
                del mapping[key]
                return
        raise KeyError(key)


def ensure_scope(
    level: int, global_dict=None, local_dict=None, resolvers=(), target=None
) -> Scope:
    """Ensure that we are grabbing the correct scope."""
    return Scope(
        level + 1,
        global_dict=global_dict,
        local_dict=local_dict,
        resolvers=resolvers,
        target=target,
    )


def _replacer(x) -> str:
    """
    Replace a number with its hexadecimal representation. Used to tag

View on GitHub (pinned to 3b7651241d)

Solutions

1. Guard deletions with a membership check: if key in dcm: del dcm[key].
2. Use dcm.maps iteration to confirm the key lives in a specific mapping before deleting.
3. Avoid mutating the internal DeepChainMap of eval/query scopes directly; let pandas manage scope lifetime.

Example fix

// before
del scope_chainmap['my_temp']  # KeyError if absent

// after
if 'my_temp' in scope_chainmap:
    del scope_chainmap['my_temp']

def safe_delete(chainmap, key):
    if key in chainmap:
        del chainmap[key]
        return True
    return False

try:
    del scope_chainmap[key]
except KeyError:
    pass  # already absent; nothing to clean

When it happens

Trigger: Internal scope cleanup calling del scope[key] for a temporary/resolver key that was never inserted or was already deleted; user code reaching into the DeepChainMap returned by an eval scope and deleting a missing key; double-deletion of the same temporary variable.

Common situations: Rare from the public API; can appear in custom resolvers or when manipulating the scope object handed to eval. Most often a secondary symptom of logic that assumes a name exists in scope when it doesn't.

Related errors

• The '@' prefix is not allowed in top-level eval calls. pleas
• name '{name}' is not defined
• invalid validation method '{method}'
• Label(s) {list(cols)} do not exist
• No accumulation for {func} implemented on BaseMaskedArray

AI-assisted analysis of pandas-dev/pandas@3b7651241d (2026-08-11). Data as JSON: /api/errors/f87b8bd24aaaea14. Report an issue: GitHub.