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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Python classes cannot inherit from C# interfaces that themselves inherit from C# interfaces with methods","articleBody":"Python classes cannot inherit from C# interfaces that themselves inherit from C# interfaces with methods:\r\n\r\n```cs\r\nnamespace A\r\n{\r\n    public interface B\r\n    {\r\n        void C();\r\n    }\r\n\r\n    public interface D : B\r\n    {\r\n    }\r\n}\r\n```\r\n\r\n```python\r\nimport clr\r\n\r\nclr.AddReference('A')\r\nimport A\r\n\r\nclass E(A.D):\r\n    __namespace__ = 'F'\r\n    def C(self):\r\n        pass\r\n```\r\n\r\nOutput:\r\n\r\n```\r\nTraceback (most recent call last):\r\n  File \"\u003cstdin\u003e\", line 6, in \u003cmodule\u003e\r\nTypeError: Failed to create Python type for F.E\r\n```\r\n\r\nExtending from `B` works. It also works if `C` is removed from `B`.\r\n\r\nPossibly related to #2511. Reverting to 3.0.3 (before 9ebfbde3) provides the moderately-more-useful error `TypeError: VTable setup of type F.E failed`.\r\n\r\nPlease do **NOT** convert this to a discussion. It is a real bug that requires fixing. As noted above, providing a definition for `C` does not affect whether the bug occurs.\r\n\r\nI have tested this with mono 6.8 and 6.12, as well as with MSCV. The latter gives the slightly-different error:\r\n\r\n```\r\nTraceback (most recent call last):\r\n  File \"\u003cstdin\u003e\", line 6, in \u003cmodule\u003e\r\n    class E(A.D):\r\nTypeError: Method 'C' in type 'F.E' from assembly 'Python.Runtime.Dynamic, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' does not have an implementation.\r\n```\r\n\r\nNote that `C` was defined as above.\r\n\r\n---\r\n\r\nAs a workaround, the following can be done...\r\n\r\n```python\r\nimport clr\r\n\r\nclr.AddReference('A')\r\nimport A\r\n\r\nclass E(A.B):\r\n    __namespace__ = 'F'\r\n\r\nclass G(E, A.D):\r\n    __namespace__ = 'F'\r\n    def C(self):\r\n        pass\r\n\r\nG().C()\r\n```\r\n\r\nAnd for some reason C has to be implemented in G and not E:\r\n\r\n```\r\nSystem.NotImplementedException: Python object does not have a 'C' method\r\n  at Python.Runtime.PythonDerivedType.InvokeMethodVoid (Python.Runtime.IPythonDerivedType obj, System.String methodName, System.String origMethodName, System.Object[] args, System.RuntimeMethodHandle methodHandle, System.RuntimeTypeHandle declaringTypeHandle) [0x00151] in \u003ce8135b23d9064b84a255057569ff100a\u003e:0 \r\n  at F.E.C () [0x00000] in \u003cd16dd79070534f72b8760f94ab2e0924\u003e:0 \r\n  at F.G._E__C () [0x00000] in \u003cd16dd79070534f72b8760f94ab2e0924\u003e:0 \r\n  at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception\u0026)\r\n  at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x0007c] in \u003c12b418a7818c4ca0893feeaaf67f1e7f\u003e:0 \r\n\r\nThe above exception was the direct cause of the following exception:\r\n\r\nTraceback (most recent call last):\r\n  File \"\u003cstdin\u003e\", line 14, in \u003cmodule\u003e\r\nSystem.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---\u003e System.NotImplementedException: Python object does not have a 'C' method\r\n  at Python.Runtime.PythonDerivedType.InvokeMethodVoid (Python.Runtime.IPythonDerivedType obj, System.String methodName, System.String origMethodName, System.Object[] args, System.RuntimeMethodHandle methodHandle, System.RuntimeTypeHandle declaringTypeHandle) [0x00151] in \u003ce8135b23d9064b84a255057569ff100a\u003e:0 \r\n  at F.E.C () [0x00000] in \u003cd16dd79070534f72b8760f94ab2e0924\u003e:0 \r\n  at F.G._E__C () [0x00000] in \u003cd16dd79070534f72b8760f94ab2e0924\u003e:0 \r\n  at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception\u0026)\r\n  at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x0007c] in \u003c12b418a7818c4ca0893feeaaf67f1e7f\u003e:0 \r\n   --- End of inner exception stack trace ---\r\n  at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x0009a] in \u003c12b418a7818c4ca0893feeaaf67f1e7f\u003e:0 \r\n  at System.RuntimeType.InvokeMember (System.String name, System.Reflection.BindingFlags bindingFlags, System.Reflection.Binder binder, System.Object target, System.Object[] providedArgs, System.Reflection.ParameterModifier[] modifiers, System.Globalization.CultureInfo culture, System.String[] namedParams) [0x007b0] in \u003c12b418a7818c4ca0893feeaaf67f1e7f\u003e:0 \r\n  at System.Type.InvokeMember (System.String name, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object target, System.Object[] args) [0x00000] in \u003c12b418a7818c4ca0893feeaaf67f1e7f\u003e:0 \r\n  at Python.Runtime.PythonDerivedType.InvokeMethodVoid (Python.Runtime.IPythonDerivedType obj, System.String methodName, System.String origMethodName, System.Object[] args, System.RuntimeMethodHandle methodHandle, System.RuntimeTypeHandle declaringTypeHandle) [0x0015d] in \u003ce8135b23d9064b84a255057569ff100a\u003e:0 \r\n  at F.G.C () [0x00000] in \u003cd16dd79070534f72b8760f94ab2e0924\u003e:0 \r\n  at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception\u0026)\r\n  at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x0007c] in \u003c12b418a7818c4ca0893feeaaf67f1e7f\u003e:0 \r\n```","author":{"url":"https://github.com/sean-anderson-seco","@type":"Person","name":"sean-anderson-seco"},"datePublished":"2024-12-09T15:11:57.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/2526/pythonnet/issues/2526"}