{"record":{"id":"d36bafb677058290","repo":"reflex-dev/reflex","slug":"unsupported-type-var-type-for-guess-type","errorCode":null,"errorMessage":"Unsupported type {var_type} for guess_type.","messagePattern":"Unsupported type (.+?) for guess_type\\.","errorType":"exception","errorClass":"TypeError","httpStatus":null,"severity":"error","filePath":"packages/reflex-base/src/reflex_base/vars/base.py","lineNumber":1116,"sourceCode":"                for inner_type in non_optional_inner_types\n            ]\n\n            union_entry = _var_subclass_matching_python_types(tuple(fixed_inner_types))\n            if union_entry is not None:\n                return self.to(union_entry.var_subclass, self._var_type)\n\n            if can_use_in_object_var(var_type):\n                return self.to(ObjectVar, self._var_type)\n\n            return self\n\n        if fixed_type is Literal:\n            args = get_args(var_type)\n            fixed_type = unionize(*(type(arg) for arg in args))\n\n        if not isinstance(fixed_type, type):\n            msg = f\"Unsupported type {var_type} for guess_type.\"\n            raise TypeError(msg)\n\n        if fixed_type is None:\n            return self.to(None)\n\n        guessed_entry = _var_subclass_matching_python_types((fixed_type,))\n        if guessed_entry is not None:\n            return self.to(guessed_entry.var_subclass, self._var_type)\n\n        if can_use_in_object_var(fixed_type):\n            return self.to(ObjectVar, self._var_type)\n\n        return self\n\n    @staticmethod\n    def _get_setter_name_for_name(\n        name: str,\n    ) -> str:\n        \"\"\"Get the name of the var's generated setter function.","sourceCodeStart":1098,"sourceCodeEnd":1134,"githubUrl":"https://github.com/reflex-dev/reflex/blob/45b8ed5ab735f8a56bbb09a42384f030eb0208e7/packages/reflex-base/src/reflex_base/vars/base.py#L1098-L1134","documentation":"Var.guess_type() inspects a Var's _var_type to pick the best Var subclass (number, string, etc.). After resolving typing.Literal and generic aliases it must end up with an actual class; if the annotation is something unresolvable (a string forward-ref, a TypeVar, a parametrized special form) it raises this TypeError.","triggerScenarios":"Calling var.guess_type() when _var_type is a non-class annotation such as a TypeVar, unparameterized generic ('list' without args in some contexts), a forward reference string, or NoneType edge cases that bypass the Literal/generic handling.","commonSituations":"Annotating state fields with unusual generics or custom classes after a reflex upgrade; TypeVars in shared base states; delayed annotations (from __future__ annotations) not yet resolvable at guess time.","solutions":["Simplify the annotation to a concrete type or Optional[concrete] and re-run","Resolve forward references: ensure the referenced types are imported/defined where the annotation is evaluated","If you need a specific behavior, cast explicitly with var.to(DesiredType) instead of guess_type","Report upstream if a legitimate builtin annotation triggers it"],"exampleFix":"# before\nclass State(rx.State):\n    items: list  # bare generic trips guess_type\n# after\nclass State(rx.State):\n    items: list[str]","handlingStrategy":"validation","validationCode":"import typing\nt = State.__annotations__['field']\nassert isinstance(typing.get_origin(t) or t, type), f'guess_type cannot handle {t}'","typeGuard":"def is_guessable(anno: object) -> bool:\n    import typing\n    t = anno\n    if typing.get_origin(t) is typing.Literal:\n        args = typing.get_args(t)\n        t = type(args[0]) if args else None\n    return isinstance(t, type)","tryCatchPattern":"try:\n    v = var.guess_type()\nexcept TypeError:\n    v = var.to(dict)  # explicit cast fallback","preventionTips":["Annotate state fields with concrete, fully-parameterized types","Avoid TypeVars and string forward refs on state fields used in the UI","Prefer var.to(T) over guess_type when you know the target type"],"tags":["reflex","var","type-annotation","typeerror"],"backgroundTag":"unsupported-type-annotation","analyzedSha":"45b8ed5ab735f8a56bbb09a42384f030eb0208e7","analyzedAt":"2026-08-28T19:25:27.644Z","schemaVersion":2},"datasetVersion":"2026-08-28T21:17:43.275Z"}