and I simply use this code to load the .NET runtime:

    import pythonnet\n\n    path = os.path.join(\"path\", \"to\", \"app\", \"lib\", \"dotnet\")\n    sys.path.insert(0, path)\n    config_path = os.path.join(path, \"MyApp.runtimeconfig.json\")\n    pythonnet.load(\"coreclr\", runtime_config=str(config_path))\n\n    import clr\n\n    clr.AddReference(\"MyApp\")

This works fine mostly, however, I noticed that if my app overrides a framework dependency e.g. upgrading System.Collections.Immutable from version 8.0.0 (provided by the framework) to 9.0.0 (provided via NuGet, but still compatible with net8.0), my application starts crashing, because the SCI version 9.0.0 cannot be loaded.

After a lot debugging, I realized that this is because the MyApp.deps.json is not considered when first initializing hostfxr therefore it only ever loads the TPA version provided by the framework. See the host.log attachment for details.

Unfortunately, it seems that hostfxr is considering Python.Runtime.dll the \"main assembly\" as can be seen here

CoreCLR path = 'C:\\path\\to\\app\\build\\dependencies\\dotnet\\shared\\Microsoft.NETCore.App\\8.0.4\\coreclr.dll', CoreCLR dir = 'C:\\path\\to\\app\\build\\dependencies\\dotnet\\shared\\Microsoft.NETCore.App\\8.0.4\\'\nLoaded library from C:\\path\\to\\app\\build\\dependencies\\dotnet\\shared\\Microsoft.NETCore.App\\8.0.4\\coreclr.dll\n--- Invoked hostpolicy [version: 8.0.4 @Commit: 2d7eea252964e69be94cb9c847b371b23e4dd470] corehost_resolve_component_dependencies = {\n  Component main assembly path: C:\\path\\to\\app\\lib\\scripts-python3.10\\pythonnet\\runtime\\Python.Runtime.dll\n}\n-- arguments_t: app_root='C:\\path\\to\\app\\lib\\scripts-python3.10\\pythonnet\\runtime\\' deps='C:\\path\\to\\app\\lib\\scripts-python3.10\\pythonnet\\runtime\\Python.Runtime.deps.json' mgd_app='C:\\path\\to\\app\\lib\\scripts-python3.10\\pythonnet\\runtime\\Python.Runtime.dll'\n

I was able to work around this by doing the following:

    import pythonnet\n\n    path = os.path.join(\"path\", \"to\", \"app\", \"lib\", \"dotnet\")\n    sys.path.insert(0, path)\n    config_path = os.path.join(path, \"MyApp.runtimeconfig.json\")\n\n   runtime = clr_loader.get_coreclr(runtime_config=str(config_path))\n    \n    pythonnet.set_runtime(runtime) \n\n    libPath = os.path.join(path, \"MyApp.dll\")\n    assembly = runtime.get_assembly(str(libPath))\n\n    print(\"Loaded \" + libPath)\n\n    # just invoke an empty function to load the library\n    func = assembly.get_function(\"MyApp.Interop.Host.Initialize\")\n\n    result = func(b\"\")\n    assert result == 0, f\"Failed to initialize MyApp.dll, error code {result}\"\n    \n    pythonnet.load(runtime)\n\n    import clr\n\n    clr.AddReference(\"Python.Runtime\")\n    clr.AddReference(\"MyApp\")

now, hostfxr loads the \"correct\" deps.json file, but I get a Python error whenever I do something that involves list or dict types:

someManagedObj.ListProperty = get_python_list()

\n

TypeError: 'list' value cannot be converted to System.Collections.Generic.IReadOnlyList`1[System.String]

\n

What am I missing here? Thank you very much!

You are not missing anything, this is simply tricky. .NET Framework didn't have this \"problem\", and Python.NET was developed against .NET Framework.

I'm not sure why the conversions are messed up in your case.

Could you see whether this pythonnet/clr-loader#66 helps? It is already merged on master, just not released, yet (as I want to integrate it back into the get_coreclr factory).

How can I add MyApp.deps.json to the hostfxr initialization sequence? #2613

Answered by filmor

siegfriedpammer-qt asked this question in Q&A

How can I add MyApp.deps.json to the hostfxr initialization sequence? #2613

siegfriedpammer-qt

Aug 26, 2025 · 1 comments · 1 reply

Answered by filmor Return to top

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siegfriedpammer-qt

Aug 26, 2025

I have the following runtimeconfig.json: { "runtimeOptions": { "tfm": "net8.0", "framework": { "name": "Microsoft.NETCore.App", "version": "8.0.0" }, "configProperties": { "System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization": false } } } and I simply use this code to load the .NET runtime: import pythonnet path = os.path.join("path", "to", "app", "lib", "dotnet") sys.path.insert(0, path) config_path = os.path.join(path, "MyApp.runtimeconfig.json") pythonnet.load("coreclr", runtime_config=str(config_path)) import clr clr.AddReference("MyApp") This works fine mostly, however, I noticed that if my app overrides a framework dependency e.g. upgrading System.Collections.Immutable from version 8.0.0 (provided by the framework) to 9.0.0 (provided via NuGet, but still compatible with net8.0), my application starts crashing, because the SCI version 9.0.0 cannot be loaded. After a lot debugging, I realized that this is because the MyApp.deps.json is not considered when first initializing hostfxr therefore it only ever loads the TPA version provided by the framework. See the host.log attachment for details. Unfortunately, it seems that hostfxr is considering Python.Runtime.dll the "main assembly" as can be seen here CoreCLR path = 'C:\path\to\app\build\dependencies\dotnet\shared\Microsoft.NETCore.App\8.0.4\coreclr.dll', CoreCLR dir = 'C:\path\to\app\build\dependencies\dotnet\shared\Microsoft.NETCore.App\8.0.4\' Loaded library from C:\path\to\app\build\dependencies\dotnet\shared\Microsoft.NETCore.App\8.0.4\coreclr.dll --- Invoked hostpolicy [version: 8.0.4 @Commit: 2d7eea252964e69be94cb9c847b371b23e4dd470] corehost_resolve_component_dependencies = { Component main assembly path: C:\path\to\app\lib\scripts-python3.10\pythonnet\runtime\Python.Runtime.dll } -- arguments_t: app_root='C:\path\to\app\lib\scripts-python3.10\pythonnet\runtime\' deps='C:\path\to\app\lib\scripts-python3.10\pythonnet\runtime\Python.Runtime.deps.json' mgd_app='C:\path\to\app\lib\scripts-python3.10\pythonnet\runtime\Python.Runtime.dll' I was able to work around this by doing the following: import pythonnet path = os.path.join("path", "to", "app", "lib", "dotnet") sys.path.insert(0, path) config_path = os.path.join(path, "MyApp.runtimeconfig.json") runtime = clr_loader.get_coreclr(runtime_config=str(config_path)) pythonnet.set_runtime(runtime) libPath = os.path.join(path, "MyApp.dll") assembly = runtime.get_assembly(str(libPath)) print("Loaded " + libPath) # just invoke an empty function to load the library func = assembly.get_function("MyApp.Interop.Host.Initialize") result = func(b"") assert result == 0, f"Failed to initialize MyApp.dll, error code {result}" pythonnet.load(runtime) import clr clr.AddReference("Python.Runtime") clr.AddReference("MyApp") now, hostfxr loads the "correct" deps.json file, but I get a Python error whenever I do something that involves list or dict types: someManagedObj.ListProperty = get_python_list() TypeError: 'list' value cannot be converted to System.Collections.Generic.IReadOnlyList`1[System.String] What am I missing here? Thank you very much!

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Answered by filmor Aug 26, 2025

You are not missing anything, this is simply tricky. .NET Framework didn't have this "problem", and Python.NET was developed against .NET Framework.

I'm not sure why the conversions are messed up in your case.

Could you see whether this pythonnet/clr-loader#66 helps? It is already merged on master, just not released, yet (as I want to integrate it back into the get_coreclr factory).

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filmor

Aug 26, 2025

Maintainer

You are not missing anything, this is simply tricky. .NET Framework didn't have this "problem", and Python.NET was developed against .NET Framework. I'm not sure why the conversions are messed up in your case. Could you see whether this pythonnet/clr-loader#66 helps? It is already merged on master, just not released, yet (as I want to integrate it back into the get_coreclr factory).

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siegfriedpammer-qt Aug 26, 2025

Author

Thank you for the fast response! You are not missing anything, this is simply tricky. Yeah, unfortunately. It seems like there is also no good way to change clr_loader or pythonnet to remove this pitfall. I found the reason for the messed up conversions. Python.Runtime.dll was loaded two times: one located in the python package, the other was a local copy from my .NET build. The decoder/encoder initialization ran only in one of those. I managed to get rid of this problem by removing the local copy in the .NET build via ExcludeAssets.

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