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My problem: I have an assembly in 2 versions and want to use them at the same time in my Python project.

The .NET libs are installed in GAC (MSIL), having the same public token:

lib.dll (1.0.0.0)
lib.dll (2.0.0.0)

In Python I want something like that:

import clr
clr.AddReference("lib, Version=1.0.0.0, ...")
from lib import Class
myClass1 = Class()
myClass1.Operation()

*magic*

clr.AddReference("lib, Version=2.0.0.0, ...")
from lib import class
myClass2 = Class()
myClass2.Operation()
myClass2.OperationFromVersion2()

*other stuff*

# both objects should be accessibly
myClass1.Operation() 
myClass2.OperationFromVersion2()

Is there a way to do that? Something with AppDomains or bindingRedirect?

Note: Of course myClass1.operationFromVersion2() can fail...

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2
  • how would you add 2 versions of assemblies to references in .NET? Commented Sep 7, 2015 at 5:56
  • 1
    I can use reflections there. Commented Oct 6, 2015 at 9:22

2 Answers 2

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4

Well I found a solution: Python for .NET also supports Reflection!

Instead of

clr.AddReference("lib, Version=1.0.0.0, ...")

You have to use

assembly1 = clr.AddReference("lib, Version=1.0.0.0, ...")

With that assembly you can use all the Reflection stuff like in C#. In my example I have to use following code (same for version 2):

from System import Type
type1 = assembly1.GetType(...)
constructor1 = type1.GetConstructor(Type.EmptyTypes)
myClass1 = constructor1.Invoke([])
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This is great answer and surely should be added to pythonnet documentation!
2

I could not get it working using the accepted answer. Here is my solution.

Instead of using PythonNet you must use the .NET framework directly:

import System

dll_ref = System.Reflection.Assembly.LoadFile(fullPath)
print(dll_ref.FullName)
print(dll_ref.Location)

Check that the correct DLL is used.

To use multiple DLLs with the same version just load it to another variable 

another_dll_ref = System.Reflection.Assembly.LoadFile(anotherFullPath)

Now you can use objects from the specified dll.

Instance of a public non-static class

some_class_type = dll_ref.GetType('MyNamespace.SomeClass')
my_instance = System.Activator.CreateInstance(some_class_type)
my_instance.a = 4 # setting attribute
my_instance.b('whatever') # calling methods

Calling a method in a public static class 

some_class_type = dll_ref.GetType('MyNamespace.SomeClass')
method = some_class_type.GetMethod('SomeMethod')
# return type and list of parameters
method.Invoke(None, [1, 2.0, '3'])

Creating a instance of a struct

some_struct_type = dll_ref.GetType('MyNamespace.SomeStruct')
my_struct = System.Activator.CreateInstance(some_struct_type)
my_struct.a = 3

(taken from my question Python for .NET: How to explicitly create instances of C# classes using different versions of the same DLL?)

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