improve GenericMixin such that it also find bound type variables in parent classes

Author: LostInDarkMath

CHANGELOG.md

@@ -1,4 +1,7 @@
 # Changelog
+## Pedantic 2.1.11
+- improve `GenericMixin` such that it also find bound type variables in parent classes
+
 ## Pedantic 2.1.10
 - added type check support for `functools.partial`
 - update dependencies

pedantic/mixins/generic_mixin.py

@@ -1,5 +1,4 @@
-from types import GenericAlias
-from typing import List, Type, TypeVar, Dict, Generic, Any, Optional
+from typing import Type, TypeVar, Dict, get_origin, get_args
 
 
 class GenericMixin:
@@ -11,7 +10,7 @@ class GenericMixin:
             >>> T = TypeVar('T')
             >>> U = TypeVar('U')
             >>> class Foo(Generic[T, U], GenericMixin):
-            ...     values: List[T]
+            ...     values: list[T]
             ...     value: U
             >>> f = Foo[str, int]()
             >>> f.type_vars
@@ -24,6 +23,8 @@ def type_var(self) -> Type:
             Get the type variable for this class.
             Use this for convenience if your class has only one type parameter.
 
+            DO NOT call this inside __init__()!
+
             Example:
                 >>> from typing import Generic, TypeVar
                 >>> T = TypeVar('T')
@@ -34,7 +35,7 @@ def type_var(self) -> Type:
                 <class 'float'>
         """
 
-        types = self._get_types()
+        types = self._get_resolved_typevars()
         assert len(types) == 1, f'You have multiple type parameters. Please use "type_vars" instead of "type_var".'
         return list(types.values())[0]  # type: ignore
 
@@ -43,55 +44,77 @@ def type_vars(self) -> Dict[TypeVar, Type]:
         """
             Returns the mapping of type variables to types.
 
+            DO NOT call this inside __init__()!
+
             Example:
                 >>> from typing import Generic, TypeVar
                 >>> T = TypeVar('T')
                 >>> U = TypeVar('U')
                 >>> class Foo(Generic[T, U], GenericMixin):
-                ...     values: List[T]
+                ...     values: list[T]
                 ...     value: U
                 >>> f = Foo[str, int]()
                 >>> f.type_vars
                 {~T: <class 'str'>, ~U: <class 'int'>}
         """
 
-        return self._get_types()
+        return self._get_resolved_typevars()
 
-    def _get_types(self) -> Dict[TypeVar, Type]:
+    def _get_resolved_typevars(self) -> Dict[TypeVar, Type]:
         """
-            See https://stackoverflow.com/questions/57706180/generict-base-class-how-to-get-type-of-t-from-within-instance/60984681#60984681
+        Do not call this inside the __init__() method, because at that point the relevant information are not present.
+        See also https://github.com/python/cpython/issues/90899'
         """
 
+        mapping: dict[TypeVar, type] = {}
+
         non_generic_error = AssertionError(
             f'{self.class_name} is not a generic class. To make it generic, declare it like: '
             f'class {self.class_name}(Generic[T], GenericMixin):...')
 
         if not hasattr(self, '__orig_bases__'):
             raise non_generic_error
 
-        generic_base = get_generic_base(obj=self)
+        def collect(base, substitutions: dict[TypeVar, type]) -> None:
+            origin = get_origin(base)
+            args = get_args(base)
+
+            if origin is None:
+                return
 
-        if not generic_base:
-            for base in self.__orig_bases__:  # type: ignore # (we checked existence above)
-                if not hasattr(base, '__origin__'):
-                    continue
+            params = getattr(origin, '__parameters__', ())
+            resolved = {}
+            for param, arg in zip(params, args):
+                resolved_arg = substitutions.get(arg, arg) if isinstance(arg, TypeVar) else arg
+                mapping[param] = resolved_arg
+                resolved[param] = resolved_arg
 
-                generic_base = get_generic_base(base.__origin__)
+            for super_base in getattr(origin, '__orig_bases__', []):
+                collect(super_base, resolved)
 
-                if generic_base:
-                    types = base.__args__
-                    break
+        # Prefer __orig_class__ if available
+        cls = getattr(self, '__orig_class__', None)
+        if cls is not None:
+            collect(base=cls, substitutions={})
         else:
-            if not hasattr(self, '__orig_class__'):
-                raise AssertionError(
-                    f'You need to instantiate this class with type parameters! Example: {self.class_name}[int]()\n'
-                    f'Also make sure that you do not call this in the __init__() method of your class! '
-                    f'See also https://github.com/python/cpython/issues/90899')
+            for base in getattr(self.__class__, '__orig_bases__', []):
+                collect(base=base, substitutions={})
 
-            types = self.__orig_class__.__args__  # type: ignore
+        # Extra safety: ensure all declared typevars are resolved
+        all_params = set()
+        for cls in self.__class__.__mro__:
+            all_params.update(getattr(cls, '__parameters__', ()))
 
-        type_vars = generic_base.__args__
-        return {v: t for v, t in zip(type_vars, types)}
+        unresolved = {param for param in all_params if param not in mapping or isinstance(mapping[param], TypeVar)}
+        if unresolved:
+            raise AssertionError(
+                f'You need to instantiate this class with type parameters! Example: {self.class_name}[int]()\n'
+                f'Also make sure that you do not call this in the __init__() method of your class!\n'
+                f'Unresolved type variables: {unresolved}\n'
+                f'See also https://github.com/python/cpython/issues/90899'
+            )
+
+        return mapping
 
     @property
     def class_name(self) -> str:
@@ -100,14 +123,6 @@ def class_name(self) -> str:
         return type(self).__name__
 
 
-def get_generic_base(obj: Any) -> Optional[GenericAlias]:
-    generic_bases = [c for c in obj.__orig_bases__ if hasattr(c, '__origin__') and c.__origin__ == Generic]
-
-    if generic_bases:
-        return generic_bases[0]  # this is safe because a class can have at most one "Generic" superclass
-
-    return None
-
 if __name__ == '__main__':
     import doctest
     doctest.testmod(verbose=False, optionflags=doctest.ELLIPSIS)

pedantic/tests/test_generic_mixin.py

@@ -103,3 +103,19 @@ class MyClass(MyMixin, Gen[int]):
 
         foo = MyClass(value=4)
         assert foo.get_type() == {T: int}
+
+    def test_resolved_type_var_inheritance(self):
+        class Foo(Generic[T]): ...
+
+        class Bar(Foo[int], Generic[U], GenericMixin): ...
+
+        bar = Bar[str]()
+        assert bar.type_vars == {T: int, U: str}
+
+    def test_resolved_type_var_inheritance_2(self):
+        class Foo(Generic[T], GenericMixin): ...
+
+        class Bar(Foo[int], Generic[U]): ...
+
+        bar = Bar[str]()
+        assert bar.type_vars == {T: int, U: str}

setup.py

@@ -15,7 +15,7 @@ def get_content_from_readme(file_name: str = 'README.md') -> str:
 
 setup(
     name="pedantic",
-    version="2.1.10",
+    version="2.1.11",
     python_requires='>=3.11.0',
     packages=find_packages(),
     install_requires=[],