fix: Add compatibility module for StrEnum and assert_never (#12)

chatkit/_compat.py

@@ -0,0 +1,21 @@
+from __future__ import annotations
+
+try:
+    from enum import StrEnum
+except ImportError:  # Python < 3.11
+    from enum import Enum
+
+    class StrEnum(str, Enum):
+        """Minimal StrEnum compatibility for Python < 3.11."""
+
+
+try:
+    from typing import assert_never
+except ImportError:  # Python < 3.11
+    from typing import NoReturn
+
+    def assert_never(arg: NoReturn) -> NoReturn:
+        raise AssertionError(f"Expected code path to be unreachable, got: {arg!r}")
+
+
+__all__ = ("StrEnum", "assert_never")

chatkit/agents.py

@@ -10,7 +10,6 @@
     Generic,
     Sequence,
     TypeVar,
-    assert_never,
     cast,
 )
 
@@ -39,6 +38,7 @@
 )
 from pydantic import BaseModel, ConfigDict, SkipValidation, TypeAdapter
 
+from ._compat import assert_never
 from .server import stream_widget
 from .store import Store, StoreItemType
 from .types import (

chatkit/errors.py

@@ -1,5 +1,6 @@
 from abc import ABC
-from enum import StrEnum
+
+from ._compat import StrEnum
 
 
 # Not a closed enum, new error codes can and will be added as needed

chatkit/server.py

@@ -3,14 +3,7 @@
 from collections.abc import AsyncIterator
 from contextlib import contextmanager
 from datetime import datetime
-from typing import (
-    Any,
-    AsyncGenerator,
-    AsyncIterable,
-    Callable,
-    Generic,
-    assert_never,
-)
+from typing import Any, AsyncGenerator, AsyncIterable, Callable, Generic
 
 import agents
 from agents.models.chatcmpl_helpers import (
@@ -24,6 +17,7 @@
 
 from chatkit.errors import CustomStreamError, StreamError
 
+from ._compat import assert_never
 from .logger import logger
 from .store import AttachmentStore, Store, StoreItemType, default_generate_id
 from .types import (

tests/helpers/mock_widget.py

@@ -2,12 +2,13 @@
 import re
 import uuid
 from datetime import datetime, timedelta
-from typing import Annotated, Any, AsyncIterator, Callable, Literal, assert_never
+from typing import Annotated, Any, AsyncIterator, Callable, Literal
 
 from agents import Agent, Runner
 from anyio import sleep
 from pydantic import BaseModel, Field, TypeAdapter
 
+from chatkit._compat import assert_never
 from chatkit.actions import Action, ActionConfig
 from chatkit.types import ThreadStreamEvent
 from chatkit.widgets import (