reflex-dev/reflex · error · TypeError

` ` only accepts children positionally.

Error message

`{definition.python_name}` only accepts children positionally.

What it means

When calling a memoized component, `children` is a reserved positional-only slot; passing `children=` as a keyword argument is rejected. Children must be given positionally, e.g. `my_memo(rx.text("hi"))`, not `my_memo(children=rx.text("hi"))`.

Solutions

Move children to positional arguments: `card(rx.text("body"), title="x")`.
If the memo should accept children as a normal prop, rename its parameter to something other than the reserved `children` handling, or restructure so children flow positionally.

Example fix

# before
card(title="x", children=rx.text("body"))

# after
card(rx.text("body"), title="x")

Defensive patterns

Strategy: validation

Validate before calling

def safe_call(memo_fn, *children, **props):
    props.pop("children", None)  # reserved: children go positionally
    return memo_fn(*children, **props)

Prevention

Never pass children= as a keyword; always give children positionally as the first arguments.
Treat 'children' as reserved like in React, but positional in Reflex.
Watch out for **props splatting dicts that contain a 'children' key.

When it happens

Trigger: Calling a memo component with a `children` keyword: `card(title="x", children=rx.text("body"))`. Raised in `_bind_function_runtime_args` at call time (including via `functools.partial`-style `partial`).

Common situations: Habits carried over from React/Next.js (`children` prop) or other component libs where children is a named prop; IDE autocompleting `children=`; copy-pasting JSX-style props into Reflex calls.

Related errors

AI-assisted analysis of reflex-dev/reflex@45b8ed5ab7 (2026-08-28). Data as JSON: /api/errors/7f0c757519e6325a. Report an issue: GitHub.

Appendix: source

Thrown at packages/reflex-base/src/reflex_base/components/memo.py:1535

    Args:
        definition: The function memo definition.
        *args: Positional arguments.
        **kwargs: Keyword arguments.

    Returns:
        The ordered arguments for the imported FunctionVar.

    Raises:
        TypeError: If the provided arguments are invalid.
    """
    children_param = _get_children_param(definition.params)
    rest_param = _get_rest_param(definition.params)

    # Validate positional children usage and reserved keywords.
    if "children" in kwargs:
        msg = f"`{definition.python_name}` only accepts children positionally."
        raise TypeError(msg)

    if rest_param is not None and rest_param.name in kwargs:
        msg = (
            f"`{definition.python_name}` captures rest props from extra keyword "
            f"arguments. Do not pass `{rest_param.name}=` directly."
        )
        raise TypeError(msg)

    if args and children_param is None:
        msg = f"`{definition.python_name}` only accepts keyword props."
        raise TypeError(msg)

    if any(not _is_component_child(child) for child in args):
        msg = (
            f"`{definition.python_name}` only accepts positional children that are "
            "`rx.Component` or `rx.Var[rx.Component]`."
        )
        raise TypeError(msg)

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