pandas-dev/pandas · error · ValueError

" " is not a supported function

Error message

"{name}" is not a supported function

What it means

Raised in FuncNode.__init__ when the requested function name is not in MATHOPS — the fixed whitelist of numpy math functions exposed through eval/query (sin, cos, tan, exp, log, expm1, log1p, sqrt, sinh, cosh, tanh, arcsin, arccos, arctan, arccosh, arcsinh, arctanh, abs, log10, floor, ceil, arctan2). FuncNode is the fallback constructor invoked when a call target is not resolvable in the user scope; if the name also misses the whitelist, this ValueError is raised and typically surfaces as the underlying cause of an UndefinedVariableError re-raise.

Solutions

1. Use only whitelisted math function names; see MATHOPS in pandas/core/computation/ops.py.
2. For np.isnan/np.isinf/np.where, compute in Python first and inject via @-local: mask = np.isnan(df['A']); df[mask].
3. Pre-resolve custom functions in scope and reference them with @ prefix only if they accept positional Series args.
4. Validate function names against MATHOPS before assembling a dynamic query string.

Example fix

// before
from pandas.core.computation.ops import FuncNode
FuncNode("isnan")
df.query("isnan(A)")

// after
mask = np.isnan(df['A'])
df[mask]
# or use the whitelist
df.query("sin(A) > 0.5")

import pandas.core.computation.ops as _ops

def is_supported_mathop(name: str) -> bool:
    return name in _ops.MATHOPS

assert is_supported_mathop(fn_name), f'{fn_name} is not a supported function; see MATHOPS'

import pandas.core.computation.ops as _ops
from typing import Any

def is_mathop_name(name: Any) -> bool:
    return isinstance(name, str) and name in _ops.MATHOPS

try:
    from pandas.core.computation.ops import FuncNode
    FuncNode('isnan')
except ValueError as e:
    if 'not a supported function' in str(e):
        mask = np.isnan(df['A'])
    else:
        raise

When it happens

Trigger: df.query('foo(A)') where 'foo' is neither in scope nor in MATHOPS (this ValueError is raised inside the fallback try, then caught and the original UndefinedVariableError is re-raised — but direct FuncNode('foo') construction surfaces it). Programmatic use of FuncNode to validate a function name.

Common situations: Typos in math function names ('arcsinh' vs 'arcsinh'). Expecting arbitrary numpy functions (np.where, np.maximum, np.isnan) to be available in eval. Building query strings dynamically and forgetting to whitelist/escape custom functions.

Related errors

• Function " " does not support keyword arguments
• Invalid function call
• cannot evaluate scalar only bool ops
• keyword error in function call
• N-dimensional objects, where N > 2, are not supported with…

AI-assisted analysis of pandas-dev/pandas@3b7651241d (2026-08-11). Data as JSON: /api/errors/6abbfdce2d817b44. Report an issue: GitHub.

Appendix: source

Thrown at pandas/core/computation/ops.py:561

class MathCall(Op):
    def __init__(self, func, args) -> None:
        super().__init__(func.name, args)
        self.func = func

    def __call__(self, env):
        # error: "Op" not callable
        operands = [op(env) for op in self.operands]  # type: ignore[operator]
        return self.func.func(*operands)

    def __repr__(self) -> str:
        operands = map(str, self.operands)
        return pprint_thing(f"{self.op}({','.join(operands)})")


class FuncNode:
    def __init__(self, name: str) -> None:
        if name not in MATHOPS:
            raise ValueError(f'"{name}" is not a supported function')
        self.name = name
        self.func = getattr(np, name)

    def __call__(self, *args) -> MathCall:
        return MathCall(self, args)

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