1768 .NET Attribute Support: Fix by rmadsen-ks · Pull Request #2032 · pythonnet/pythonnet

rmadsen-ks · 2022-11-30T09:30:11Z

Added support for specifying .NET attributes using clr_attributes. Classes, properties and methods can specify this value.
Added support for Attribute shorthand without the "Attribute" ending.
Added unit test verifying the behavior

Checklist

Check all those that are applicable and complete.

Make sure to include one or more tests for your change
If an enhancement PR, please create docs and at best an example
Ensure you have signed the .NET Foundation CLA
Add yourself to AUTHORS
Updated the CHANGELOG

- Added support for specifying .NET attributes using __clr_attributes__. Classes, properties and methods can specify this value. - Added support for Attribute shorthand without the "Attribute" ending. - Added unit test verifying the behavior

lostmsu · 2022-11-30T21:13:35Z

+            Type attribute = tp[0].As<Type>();
+            if (typeof(Attribute).IsAssignableFrom(attribute) == false)
+            {
+                throw new Exception($"This type cannot be used as an attribute type: {attribute}");


The exception type must be specific.

Also, please add a test for this scenario to ensure it does not lead to a fatal error. You might need to raise a Python exception instead.

lostmsu · 2022-11-30T21:14:31Z

+            // in python there is no difference. But luckily there is rarely a conflict, so we can treat
+            // named arguments and named properties or fields the same way.
+            var tp = new PyTuple(attr);
+            Type attribute = tp[0].As<Type>();


Same as below, you need to handle the scenario where the object passed here is not actually a Type properly.

lostmsu · 2022-11-30T21:15:01Z

+            var args = tp[1].As<PyObject[]>();
+            var dict = new PyDict(tp[2]);


lostmsu · 2022-11-30T21:15:45Z

+            var dict = new PyDict(tp[2]);
+            var dict2 = new Dictionary<string, PyObject>();


Please name variables with descriptive names.

lostmsu · 2022-11-30T21:20:01Z

+            var allConstructors = attribute.GetConstructors();
+            foreach (var constructor in allConstructors)


This reimplements our overloading logic. We definitely do not want to do that. Instead the Python side should use some simple mechanism to set the fields. For example, there could be a .with(attributes: dict[str, Any]) -> Self method, that would set values of the fields/properties from the dictionary.

E.g. DllImport("kernel32").with({"CharSet": Auto}) (just an example, a different way to do this could also be acceptable).

I think that might make sense for properties. I just wanted the call to be analogous to how it is invoked in C#, since people will always be finding the C# documentation/ code samples for how those attributes are used. e.g

[AttributeTest("UnnamedArg", NamedArg : "x", NamedProperty="y")]

This would now be used like this:

AttributeTest("UnnamedArg", NamedArg = "x", NamedProperty="y")

But you are suggesting this instead?

AttributeTest("UnnamedArg", NamedArg = "x").with({"NamedProperty": "y"})

@rmadsen-ks correct. The reason is that we don't want to maintain yet another overload resolution handler. That's one of the most complicated parts of C# that we try to mirror.

Ok, so you are not talking so much about changing these specific lines, but rather changing how the data for that is stored?

I am not sure we can use the other overload resolution handler, because that is for runtime overload resolution, right? this is compile/load time and the data we can put into those attributes is limited.

@rmadsen-ks since this is running in Python, it is runtime.

I believe you should be able to use MethodBinder.Bind which returns a Binding.

Unless I'm completely confused, The selected overload gets compiled to IL by System.Reflection.Emit. That is what the returned CustomAttributeBuilder is for.

@rmadsen-ks not sure I understand this comment.

MethodBinder.Bind performs basically what your loop performs: selects the method from the list of overloads, and returns it + the arguments for it as .NET would see them (e.g. an instance of Binding), which you can then use in the CustomAttributeBuilder constructor.

I am talking about replacing the whole loop with an invocation to MethodBinder.Bind

lostmsu · 2022-11-30T21:24:32Z

+            var qname2 = qname + "Attribute";
+            var type2 = AssemblyManager.LookupTypes(qname2).FirstOrDefault(t => t.IsPublic);
+            if (type2 != null)
+            {
+                var str = "def {2}__AttributeBuilder(*args, **kwargs):\n"
+                          + "   import {1}\n"
+                          + "   return ({0}, args, kwargs)\n";
+                str = string.Format(str, qname2, _namespace, name);
+                PythonEngine.Exec(str);
+                using var attributeData = PythonEngine.Eval(name + "__AttributeBuilder");
+                var pinnedAttributeData = attributeData.NewReferenceOrNull();
+                StoreAttribute(name, pinnedAttributeData.Borrow());
+                return new NewReference(pinnedAttributeData);
+            }
+


This seems overly complicated. Can't you just do what the code above does for type lookup, and just add another StoreAttribute for the alias?

So for e.g BrowsableAttribute, this generates a function which takes the arguments and stores it as a tuple along with the type name. That way we can reconstruct which arguments are used for creating the attribute when later generating the code.

The reason it needs to be a function is that whenever e.g Browsableis invoked, it needs to generate a new tuple because the arguments are not the same every time.

lostmsu · 2022-11-30T21:36:00Z

@rmadsen-ks btw generally speaking the code down at that level should not be using PyObject unless strictly necessary. Instead, BorrowedReference and NewReference should be used in conjunction with Runtime.Py... methods.

rmadsen-ks · 2022-11-30T21:53:37Z

@rmadsen-ks btw generally speaking the code down at that level should not be using PyObject unless strictly necessary. Instead, BorrowedReference and NewReference should be used in conjunction with Runtime.Py... methods.

Which code do you mean specifically? This code used PyDict before I arrived.. :)

lostmsu · 2025-04-11T04:49:54Z

Closing as the requested changes were not implemented

1768 .NET Attribute Support: Fix

42ee643

- Added support for specifying .NET attributes using __clr_attributes__. Classes, properties and methods can specify this value. - Added support for Attribute shorthand without the "Attribute" ending. - Added unit test verifying the behavior

lostmsu requested changes Nov 30, 2022

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lostmsu closed this Apr 11, 2025

		var args = tp[1].As<PyObject[]>();
		var dict = new PyDict(tp[2]);

		var dict = new PyDict(tp[2]);
		var dict2 = new Dictionary<string, PyObject>();

		var allConstructors = attribute.GetConstructors();
		foreach (var constructor in allConstructors)

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rmadsen-ks commented Nov 30, 2022

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lostmsu commented Nov 30, 2022

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rmadsen-ks commented Nov 30, 2022

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lostmsu commented Apr 11, 2025

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rmadsen-ks Nov 30, 2022 •

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