Added typevar defaults to (Base)ExceptionGroup (#147)

This allows an `except BaseExceptionGroup` clause to pass Pyright >= 1.1.399.

Fixes #146.

Author: mikenerone

.pre-commit-config.yaml

@@ -16,7 +16,7 @@ repos:
   - id: trailing-whitespace
 
 - repo: https://github.com/astral-sh/ruff-pre-commit
-  rev: v0.11.4
+  rev: v0.11.7
   hooks:
     - id: ruff
       args: [--fix, --show-fixes]

CHANGES.rst

@@ -7,6 +7,10 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
 
 - Added ``**kwargs`` to function and method signatures as appropriate to match the
   signatures in the standard library
+- In line with the stdlib typings in typeshed, updated ``(Base)ExceptionGroup`` generic
+  types to define defaults for their generic arguments (defaulting to
+  ``BaseExceptionGroup[BaseException]`` and ``ExceptionGroup[Exception]``)
+  (PR by @mikenerone)
 
 **1.2.2**
 

pyproject.toml

@@ -18,6 +18,9 @@ authors = [{name = "Alex Grönholm", email = "[email protected]"}]
 license = {file = "LICENSE"}
 requires-python = ">=3.7"
 dynamic = ["version"]
+dependencies = [
+    "typing-extensions >= 4.6.0; python_version < '3.13'",  # Needed for default (Base)ExceptionGroup generics
+]
 
 [project.urls]
 Changelog = "https://github.com/agronholm/exceptiongroup/blob/main/CHANGES.rst"

src/exceptiongroup/_exceptions.py

@@ -1,13 +1,21 @@
 from __future__ import annotations
 
+import sys
 from collections.abc import Callable, Sequence
 from functools import partial
 from inspect import getmro, isclass
 from typing import TYPE_CHECKING, Generic, Type, TypeVar, cast, overload
 
-_BaseExceptionT_co = TypeVar("_BaseExceptionT_co", bound=BaseException, covariant=True)
+if sys.version_info < (3, 13):
+    from typing_extensions import TypeVar
+
+_BaseExceptionT_co = TypeVar(
+    "_BaseExceptionT_co", bound=BaseException, covariant=True, default=BaseException
+)
 _BaseExceptionT = TypeVar("_BaseExceptionT", bound=BaseException)
-_ExceptionT_co = TypeVar("_ExceptionT_co", bound=Exception, covariant=True)
+_ExceptionT_co = TypeVar(
+    "_ExceptionT_co", bound=Exception, covariant=True, default=Exception
+)
 _ExceptionT = TypeVar("_ExceptionT", bound=Exception)
 # using typing.Self would require a typing_extensions dependency on py<3.11
 _ExceptionGroupSelf = TypeVar("_ExceptionGroupSelf", bound="ExceptionGroup")

tests/check_types.py

@@ -13,6 +13,11 @@
 # expected type error when passing a BaseException to ExceptionGroup
 ExceptionGroup("", (KeyboardInterrupt(),))  # type: ignore[type-var]
 
+# (Base)ExceptionGroup types should reflect these defaults for their generic arguments
+default_base_eg: BaseExceptionGroup = BaseExceptionGroup("", (KeyboardInterrupt(),))
+default_eg: ExceptionGroup = ExceptionGroup("", (ValueError(),))
+assert_type(default_base_eg, BaseExceptionGroup[BaseException])
+assert_type(default_eg, ExceptionGroup[Exception])
 
 # code snippets from the README