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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Implicit List conversion breaks backwards compatibility + numpy support","articleBody":"### Environment\r\n\r\nComputer 1:\r\n-   Pythonnet version: 2.3, installed via pip I think\r\n-   Python version: 2.7.12\r\n-   Operating System: Ubuntu 16.04.2\r\n\r\nComputer 2:\r\n-   Pythonnet version: manual build on master from commit ce14424 (currently 11 commits behind)\r\n-   Python version: 2.7.12\r\n-   Operating System: Ubuntu 16.04.2\r\n\r\n### Details\r\n\r\nDescription: Python calls .NET function which returns a List\u003cMyType\u003e.  Python then passes the return value, without modification, to a second .NET function which accepts a List\u003cMyType\u003e.  Computer 1 executes this code just fine.  On Computer 2, there is no .NET function found that matches the arguments because the return value of the .NET function has been transformed into a Python list.\r\n\r\nPython code:\r\n```\r\nimport clr\r\nfrom MyDotNetProject import PythonInterop\r\n\r\nx = PythonInterop.GetDoubleList()\r\nPythonInterop.PrintDoubleList(x)\r\n```\r\n\r\n.NET code:\r\n```\r\n    public class PythonInterop\r\n    {\r\n        public static List\u003cDouble\u003e GetDoubleList() {\r\n            var result = new List\u003cDouble\u003e();\r\n            result.Add(1);\r\n            result.Add(2);\r\n            result.Add(3);\r\n            return result;\r\n        }\r\n\r\n        public static void PrintDoubleList(List\u003cDouble\u003e list) {\r\n            Console.WriteLine(\"You list has \" + list.Count + \" elements\");\r\n        }\r\n    }\r\n```\r\n\r\nThe Python code works fine on Computer 1.  On Computer 2, the PrintDoubleList call produces\r\nTypeError: No method matches given arguments\r\n\r\nIf I print type(x) in Python, Computer 1 gives me a .NET List type while Computer 2 gives me a Python list.  I can print x.Count on Computer 1, but I get a missing attribute error on Computer 2.\r\n\r\nIf I build manually from the 2.3 tag, I get the same (good) behavior as on Computer 1.\r\n\r\nIt seems that some feature has been partially added to automatically convert .NET objects into Python objects when possible.  I suppose this is ok (though I would prefer that not happen because I don't want the mandatory performance hit of converting even when I don't want to convert), but if that's the intention, there *must* be automatic conversion of Python objects to .NET objects also.  One without the other is a critical bug.","author":{"url":"https://github.com/BenjaminPelletier","@type":"Person","name":"BenjaminPelletier"},"datePublished":"2017-07-20T00:03:42.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":37},"url":"https://github.com/514/pythonnet/issues/514"}