reflex-dev/reflex · error · TypeError

Unexpected keyword arguments: {unexpected_kwargs}

Error message

Unexpected keyword arguments: {unexpected_kwargs}

What it means

ComputedVar._replace rebuilds the var via type(self)(**field_values) and only forwards a known set of fields (fget, initial_value, cache, deps, auto_deps, interval, backend, _js_expr, _var_type/_return_type, etc.). If the dataclass was constructed with extra attribute kwargs that _replace does not propagate, or a caller passes unknown kwargs, the reconstruction raises this TypeError. It indicates an internal/API mismatch in how a ComputedVar is being rebuilt.

Source

Thrown at packages/reflex-base/src/reflex_base/vars/base.py:2465

            "fget": kwargs.pop("fget", self._fget),
            "initial_value": kwargs.pop("initial_value", self._initial_value),
            "cache": kwargs.pop("cache", self._cache),
            "deps": kwargs.pop("deps", copy.copy(self._static_deps)),
            "auto_deps": kwargs.pop("auto_deps", self._auto_deps),
            "interval": kwargs.pop("interval", self._update_interval),
            "backend": kwargs.pop("backend", self._backend),
            "_js_expr": kwargs.pop("_js_expr", self._js_expr),
            "_var_type": kwargs.pop("_var_type", self._var_type),
            "_var_data": kwargs.pop(
                "_var_data", VarData.merge(self._var_data, merge_var_data)
            ),
            "return_type": kwargs.pop("return_type", self._var_type),
        }

        if kwargs:
            unexpected_kwargs = ", ".join(kwargs.keys())
            msg = f"Unexpected keyword arguments: {unexpected_kwargs}"
            raise TypeError(msg)

        return type(self)(**field_values)

    @property
    def _cache_attr(self) -> str:
        """The attribute used to cache the value on the instance.

        Returns:
            An attribute name.
        """
        return f"__cached_{self._js_expr}"

    @property
    def _last_updated_attr(self) -> str:
        """The attribute used to store the last updated timestamp.

        Returns:
            An attribute name.

View on GitHub (pinned to 45b8ed5ab7)

Solutions

1. If subclassing ComputedVar, override _replace to include your extra fields, or avoid extra init kwargs
2. Run uv sync / align reflex and reflex-base versions so _replace matches the constructor
3. Update your fork/vendored copy if you patched ComputedVar fields without updating _replace

Example fix

# before
class MyComputedVar(rx.vars.ComputedVar):
    def __init__(self, fget, my_extra=None, **kwargs):
        super().__init__(fget, **kwargs)
        self.my_extra = my_extra
# later: some_var._replace(merge_var_data=...) -> TypeError

# after
class MyComputedVar(rx.vars.ComputedVar):
    def __init__(self, fget, my_extra=None, **kwargs):
        super().__init__(fget, **kwargs)
        self.my_extra = my_extra

    def _replace(self, **kwargs):
        kwargs.setdefault('my_extra', self.my_extra)
        return super()._replace(**kwargs)

import inspect

def replace_safe(cv, **kwargs) -> 'ComputedVar':
    import reflex.vars as rx_vars
    params = set(inspect.signature(type(cv).__init__).parameters)
    safe = {k: v for k, v in kwargs.items() if k in params or k in {'merge_var_data', 'partial', 'initial_value', '_js_expr', 'return_type'}}
    return cv._replace(**safe)

try:
    new_var = cv._replace(**opts)
except TypeError as e:
    if 'Unexpected keyword arguments' in str(e):
        new_var = cv._replace(merge_var_data=opts.get('merge_var_data'))
    else:
        raise

When it happens

Trigger: Calling ComputedVar._replace(...) with a kwarg not in its supported set; creating a ComputedVar subclass whose __init__ accepts extra kwargs not handled by _replace, then applying _replace (e.g. during var-data merging in the compiler); version skew where _replace's field list differs from the constructor's accepted kwargs.

Common situations: Subclassing ComputedVar with additional constructor parameters; running mismatched reflex/reflex-base workspace versions so the field list is out of sync; internal compiler paths calling _replace on custom var subclasses.

Related errors

• Expected _js_expr to be a string, got value {self._js_expr!r
• LiteralVar subclasses must implement the _var_value property
• LiteralVar subclasses must implement the json method.
• Unexpected keyword arguments: {tuple(kwargs)}
• ComputedVar dependencies must be Var instances or var names

AI-assisted analysis of reflex-dev/reflex@45b8ed5ab7 (2026-08-28). Data as JSON: /api/errors/6ac24a47699dcc42. Report an issue: GitHub.