chore(internal): fix typing util function

src/anthropic/_utils/_typing.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from typing import Any, cast
+from typing import Any, TypeVar, cast
 from typing_extensions import Required, Annotated, get_args, get_origin
 
 from .._types import InheritsGeneric
@@ -23,6 +23,12 @@ def is_required_type(typ: type) -> bool:
     return get_origin(typ) == Required
 
 
+def is_typevar(typ: type) -> bool:
+    # type ignore is required because type checkers
+    # think this expression will always return False
+    return type(typ) == TypeVar  # type: ignore
+
+
 # Extracts T from Annotated[T, ...] or from Required[Annotated[T, ...]]
 def strip_annotated_type(typ: type) -> type:
     if is_required_type(typ) or is_annotated_type(typ):
@@ -49,6 +55,15 @@ class MyResponse(Foo[bytes]):
 
     extract_type_var(MyResponse, bases=(Foo,), index=0) -> bytes
     ```
+
+    And where a generic subclass is given:
+    ```py
+    _T = TypeVar('_T')
+    class MyResponse(Foo[_T]):
+        ...
+
+    extract_type_var(MyResponse[bytes], bases=(Foo,), index=0) -> bytes
+    ```
     """
     cls = cast(object, get_origin(typ) or typ)
     if cls in generic_bases:
@@ -75,6 +90,18 @@ class MyResponse(Foo[bytes]):
                 f"Does {cls} inherit from one of {generic_bases} ?"
             )
 
-        return extract_type_arg(target_base_class, index)
+        extracted = extract_type_arg(target_base_class, index)
+        if is_typevar(extracted):
+            # If the extracted type argument is itself a type variable
+            # then that means the subclass itself is generic, so we have
+            # to resolve the type argument from the class itself, not
+            # the base class.
+            #
+            # Note: if there is more than 1 type argument, the subclass could
+            # change the ordering of the type arguments, this is not currently
+            # supported.
+            return extract_type_arg(typ, index)
+
+        return extracted
 
     raise RuntimeError(f"Could not resolve inner type variable at index {index} for {typ}")

tests/test_utils/test_typing.py

@@ -0,0 +1,78 @@
+from __future__ import annotations
+
+from typing import Generic, TypeVar, cast
+
+from anthropic._utils import extract_type_var_from_base
+
+_T = TypeVar("_T")
+_T2 = TypeVar("_T2")
+_T3 = TypeVar("_T3")
+
+
+class BaseGeneric(Generic[_T]):
+    ...
+
+
+class SubclassGeneric(BaseGeneric[_T]):
+    ...
+
+
+class BaseGenericMultipleTypeArgs(Generic[_T, _T2, _T3]):
+    ...
+
+
+class SubclassGenericMultipleTypeArgs(BaseGenericMultipleTypeArgs[_T, _T2, _T3]):
+    ...
+
+
+class SubclassDifferentOrderGenericMultipleTypeArgs(BaseGenericMultipleTypeArgs[_T2, _T, _T3]):
+    ...
+
+
+def test_extract_type_var() -> None:
+    assert (
+        extract_type_var_from_base(
+            BaseGeneric[int],
+            index=0,
+            generic_bases=cast("tuple[type, ...]", (BaseGeneric,)),
+        )
+        == int
+    )
+
+
+def test_extract_type_var_generic_subclass() -> None:
+    assert (
+        extract_type_var_from_base(
+            SubclassGeneric[int],
+            index=0,
+            generic_bases=cast("tuple[type, ...]", (BaseGeneric,)),
+        )
+        == int
+    )
+
+
+def test_extract_type_var_multiple() -> None:
+    typ = BaseGenericMultipleTypeArgs[int, str, None]
+
+    generic_bases = cast("tuple[type, ...]", (BaseGenericMultipleTypeArgs,))
+    assert extract_type_var_from_base(typ, index=0, generic_bases=generic_bases) == int
+    assert extract_type_var_from_base(typ, index=1, generic_bases=generic_bases) == str
+    assert extract_type_var_from_base(typ, index=2, generic_bases=generic_bases) == type(None)
+
+
+def test_extract_type_var_generic_subclass_multiple() -> None:
+    typ = SubclassGenericMultipleTypeArgs[int, str, None]
+
+    generic_bases = cast("tuple[type, ...]", (BaseGenericMultipleTypeArgs,))
+    assert extract_type_var_from_base(typ, index=0, generic_bases=generic_bases) == int
+    assert extract_type_var_from_base(typ, index=1, generic_bases=generic_bases) == str
+    assert extract_type_var_from_base(typ, index=2, generic_bases=generic_bases) == type(None)
+
+
+def test_extract_type_var_generic_subclass_different_ordering_multiple() -> None:
+    typ = SubclassDifferentOrderGenericMultipleTypeArgs[int, str, None]
+
+    generic_bases = cast("tuple[type, ...]", (BaseGenericMultipleTypeArgs,))
+    assert extract_type_var_from_base(typ, index=0, generic_bases=generic_bases) == int
+    assert extract_type_var_from_base(typ, index=1, generic_bases=generic_bases) == str
+    assert extract_type_var_from_base(typ, index=2, generic_bases=generic_bases) == type(None)