reflex-dev/reflex · error · ValueError

the function names should be str names of functions in the s

Error message

the function names should be str names of functions in the specified transformer: {library!r}

What it means

Raised by reflex_components_code.shiki_code_block.create_transformer when one of the function names passed in `fns` is not a Python str. The transformer API compiles function names into FunctionStringVar instances, so only string names of exported functions in the target transformer library are accepted.

Source

Thrown at packages/reflex-components-code/src/reflex_components_code/shiki_code_block.py:668

        return imports

    @classmethod
    def create_transformer(cls, library: str, fns: list[str]) -> ShikiBaseTransformers:
        """Create a transformer from a third party library.

        Args:
            library: The name of the library.
            fns: The str names of the functions/callables to invoke from the library.

        Returns:
            A transformer for the specified library.

        Raises:
            ValueError: If a supplied function name is not valid str.
        """
        if any(not isinstance(fn_name, str) for fn_name in fns):
            msg = f"the function names should be str names of functions in the specified transformer: {library!r}"
            raise ValueError(msg)
        return ShikiBaseTransformers(
            library=library,
            fns=[FunctionStringVar.create(fn) for fn in fns],  # pyright: ignore [reportCallIssue]
        )

    def _render(self, props: dict[str, Any] | None = None):
        """Renders the component with the given properties, processing transformers if present.

        Args:
            props: Optional properties to pass to the render function.

        Returns:
            Rendered component output.
        """
        # Ensure props is initialized from class attributes if not provided
        props = props or {
            attr.rstrip("_"): getattr(self, attr) for attr in self.get_props()
        }

View on GitHub (pinned to 45b8ed5ab7)

Solutions

Pass the names of the transformer functions as plain strings, e.g. fns=['rehypeSlug']
If building fns programmatically, coerce each entry with str(fn) only if it really is a name
Check for None entries before calling create_transformer

Example fix

// before
create_transformer("rehype-slug", fns=[rehype_slug])

// after
create_transformer("rehype-slug", fns=["rehypeSlug"])

Defensive patterns

Strategy: validation

Validate before calling

fns = [fn for fn in fns if fn is not None]
assert all(isinstance(fn, str) for fn in fns), fns

Type guard

def is_fn_names(fns: list) -> bool:
    return all(isinstance(fn, str) for fn in fns)

Prevention

Always quote transformer function names as strings
Lint for non-str entries when building fns dynamically

When it happens

Trigger: Calling create_transformer('rehype-remark', fns=[SomeFunction]) or passing a callable, None, or imported function object instead of the string function name in the `fns` list.

Common situations: Developers import a transformer function directly (e.g. `import rehypeSlug from ...`) and pass the imported object instead of the string 'rehypeSlug'; or they build the fns list dynamically and accidentally include None.

Understand the failure class

Background: Invalid argument type errors: "must be of type string", "expected X, got Y", and ERR_INVALID_ARG_TYPE explained — this error's family across 15 libraries.

Related errors

AI-assisted analysis of reflex-dev/reflex@45b8ed5ab7 (2026-08-28). Data as JSON: /api/errors/4f68d8b75b413c7a. Report an issue: GitHub.