microsoft/semantic-kernel · error · TypeError

Orchestration must have two type parameters.

Error message

Orchestration must have two type parameters.

What it means

_set_types reads the explicit generic arguments from __orig_class__ (set when you instantiate like MyOrchestration[str, str](...)). It accepts exactly one or two args (one defaults the output type); any other count is invalid. This branch fires when __orig_class__ is present but its __args__ length is not 1 or 2.

Source

Thrown at python/semantic_kernel/agents/orchestration/orchestration_base.py:169

        my_orchestration = MyOrchestration(...)
        ```
        The type parameters can be inferred from the `__orig_bases__` attribute.
        """
        if all([self.t_in is not None, self.t_out is not None]):
            return

        try:
            args = self.__orig_class__.__args__  # type: ignore[attr-defined]
            if len(args) == 1:
                self.t_in = args[0]
                self.t_out = DefaultTypeAlias  # type: ignore[assignment]
            elif len(args) == 2:
                self.t_in = args[0]
                self.t_out = args[1]
            else:
                raise TypeError("Orchestration must have two type parameters.")
        except AttributeError:
            args = get_args(self.__orig_bases__[0])  # type: ignore[attr-defined]

            if len(args) != 2:
                raise TypeError("Orchestration must be subclassed with two type parameters.")
            self.t_in = args[0] if isinstance(args[0], type) else getattr(args[0], "__default__", None)  # type: ignore[assignment]
            self.t_out = args[1] if isinstance(args[1], type) else getattr(args[1], "__default__", None)  # type: ignore[assignment]

        if any([self.t_in is None, self.t_out is None]):
            raise TypeError("Orchestration must have concrete types for all type parameters.")

    async def invoke(
        self,
        task: str | DefaultTypeAlias | TIn,
        runtime: CoreRuntime,
    ) -> OrchestrationResult[TOut]:
        """Invoke the multi-agent orchestration.

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Parameterize with one or two concrete types: `MyOrchestration[str]` or `MyOrchestration[str, str]`.
2. If your subclass declares its own TypeVars, ensure exactly one or two are exposed.
3. Avoid empty subscripts; rely on defaults by omitting the subscript entirely when appropriate.

Example fix

// before
orch = MyOrchestration[str, int, float](members)  # 3 args -> raises

// after
orch = MyOrchestration[str, str](members)

# Parameterize with one or two concrete types
orch = MyOrchestration[str, str](members)  # or MyOrchestration[str](members)

from typing import get_args

def has_valid_arity(cls) -> bool:
    args = getattr(getattr(cls, "__orig_class__", None), "__args__", ())
    return len(args) in (1, 2)

When it happens

Trigger: Instantiating an orchestration subclass with the wrong number of explicit type parameters, e.g. `MyOrchestration[]` or a subclass declaration that yields zero/three-or-more args on __orig_class__.__args__.

Common situations: Typo in generic parameterization, an empty subscript, or a custom subclass that accidentally parameterizes with three TypeVars. Misconfigured metaclass/generic machinery producing unexpected __args__.

Related errors

• Orchestration must have concrete types for all type paramete
• Orchestration must be subclassed with two type parameters.
• The members list cannot be empty.
• Configuration not found, please setup the notebooks first us
• AZURE_OPENAI_ENDPOINT is not set.

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/f695dc34c91f1ee3. Report an issue: GitHub.