Calling C# code from python using pythonnet

Question

Following is the C# code. How do I call the GenericMethod() inside the NonGenericClass from Python using pythonnet?

namespace CSharpTestCode
{
    public interface Person
    {
    }

    public class Employee : Person
    {
    }

    public class TempGenericClass<T>
    {
    }

    public class NonGenericClass
    {
        public static T GenericMethod<T>(TempGenericClass<T> tempGeneric) where T : class, Person
        {
            return null;
        }
    }
}

Python code that I tried:

import clr
clr.AddReference(r'\Documents\visual studio 2015\Projects\SamplePythonApp\CSharpTestCode\bin\Debug\CSharpTestCode.dll')
from CSharpTestCode import *

genericMethod = NonGenericClass.GenericMethod(TempGenericClass[Employee]())

Error that I got:

Unhandled Exception: System.ArgumentException: GenericArguments[0], 'CSharpTestCode.TempGenericClass`1[CSharpTestCode.Employee]', on 'T GenericMethod[T](CSharpTestCode.TempGenericClass`1[T])' violates the constraint of type 'T'. ---> System.Security.VerificationException: Method CSharpTestCode.NonGenericClass.GenericMethod: type argument 'CSharpTestCode.TempGenericClass`1[CSharpTestCode.Employee]' violates the constraint of type parameter 'T'.
   at System.RuntimeMethodHandle.GetStubIfNeeded(RuntimeMethodHandleInternal method, RuntimeType declaringType, RuntimeType[] methodInstantiation)
   at System.Reflection.RuntimeMethodInfo.MakeGenericMethod(Type[] methodInstantiation)
   --- End of inner exception stack trace ---
   at System.RuntimeType.ValidateGenericArguments(MemberInfo definition, RuntimeType[] genericArguments, Exception e)
   at System.Reflection.RuntimeMethodInfo.MakeGenericMethod(Type[] methodInstantiation)
   at Python.Runtime.MethodBinder.MatchParameters(MethodInfo[] mi, Type[] tp)
   at Python.Runtime.MethodBinder.Bind(IntPtr inst, IntPtr args, IntPtr kw, MethodBase info, MethodInfo[] methodinfo)
   at Python.Runtime.MethodBinder.Invoke(IntPtr inst, IntPtr args, IntPtr kw, MethodBase info, MethodInfo[] methodinfo)
   at Python.Runtime.MethodObject.Invoke(IntPtr target, IntPtr args, IntPtr kw, MethodBase info)
   at Python.Runtime.MethodBinding.tp_call(IntPtr ob, IntPtr args, IntPtr kw)

Do you mean an embedded IronPython interpreter? Otherwise you can't call it directly, you have to expose it somehow (many different ways for that) — UnholySheep, Jul 18 '17 at 14:52
I'm using pythonnet. I'm trying to build this code as class library and python will access this code through .dll — Developer, Jul 18 '17 at 14:53
I don't know the python syntax to call this method since it has generic type parameter in both method name and in method argument — Developer, Jul 18 '17 at 14:54
This related question may help you: https://stackoverflow.com/questions/7367976/calling-a-c-sharp-library-from-python — bavaza, Jul 18 '17 at 15:08
@bavaza I already gone through this question. But that's not what I required — Developer, Jul 18 '17 at 15:10
Did you look at Generics section of pythonnet tutorial? http://www.python4.net — denfromufa, Jul 18 '17 at 20:03
@denfromufa I read that page too. but they didn't specified my requirement — Developer, Jul 19 '17 at 08:21
but did you even try calling this generic method? if yes, can you show the error that you are getting? — denfromufa, Jul 19 '17 at 21:44
@denfromufa I added the python code that I tried along with the exception that I received. can you please refer the edited question? — Developer, Jul 20 '17 at 10:29
Reading the error message, I'm guessing pythonnet was not able to resolve that `Employee` is a `Person`. Care to remove the constraint from `NonGenericClass.GenericMethod` and try again? Alternatively, call `TempGenericClass[Person]()` — bavaza, Jul 20 '17 at 12:28
But I need to find some way to resolve this. I'm using a .dll for my project. In that, few methods are defined like this. I need to call those methods from my python project. — Developer, Jul 20 '17 at 12:44
@Developer - I suggested the above as part of the debug process. — bavaza, Jul 20 '17 at 13:08

denfromufa · Accepted Answer · 2017-07-21T06:55:33.347

I should admit that pythonnet is not supposed to crash CPython interpreter even on this bad example of generic call with invalid arguments to the method.

Here is how to properly make your generic calls with pythonnet, notice how passing wrong types fails properly:

In [3]: NonGenericClass.GenericMethod[Person](TempGenericClass[Person]())


In [4]: NonGenericClass.GenericMethod[Employee](TempGenericClass[Employee]())


In [5]: NonGenericClass.GenericMethod[Person](TempGenericClass[Employee]())
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-5-d13751f7586f> in <module>()
----> 1 NonGenericClass.GenericMethod[Person](TempGenericClass[Employee]())

TypeError: No method matches given arguments


In [6]: NonGenericClass.GenericMethod[Employee](TempGenericClass[Person]())
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-04c3c0db6c6b> in <module>()
----> 1 NonGenericClass.GenericMethod[Employee](TempGenericClass[Person]())

TypeError: No method matches given arguments

Calling C# code from python using pythonnet

1 Answers1