Possible causes for ModuleNotFoundError with .NET Framework DLL.

[draustin]

Environment

• Pythonnet version: 3.03
• Python version: 3.11.7
• Operating System: Windows 11 Pro
• .NET Runtime: DotNetVersions reports

Currently installed "classic" .NET Versions in the system:
4.0.0.0
4.8.09032

Details

In Python, I am trying to use a .NET DLL supplied by a hardware vendor ("Suragus"). The DLL targets .NET Framework 4.6.1. I can add it as a reference, see its references, and load it, but I get a ModuleNotFoundError when I import a namespace that it provides.

I am investigating three possible causes of the issue.

1. Does Pythonnet support the use of DLLs targeting .NET Framework 4.6.1? I saw this closed issue, but am not sure whether it refers to the target version of a .NET DLL, or the runtime, or both. I cannot find a definitive statement of the Pythonnet's compatibility with the target version of a .NET DLL.
2. My lack of a runtimeconfig.json file. The vendor has not supplied one. As above, I have .NET Framework 4.0 and 4.8 on my system. Could Pythonnet be selecting 4.0? The output from get_runtime_info does not say. The vendor states that .NET Framework 4.6.1 or above is required.
3. A missing referenced DLL. The DLL that I am trying to load references a DLL that is not present. The vendor assures me that this DLL is not necessary, but maybe it presents a problem for Pythonnet? The assembly can be added and loaded (see code below).

I realize that this is partly a support request, but it also relates to the completeness of documentation and specificity of error messages, which is why I'm posting it here.

Here is the code that I am using to investigate. I have described the output in comments, but cannot share it in full.

import pythonnet as pn
import clr

print(pn.get_runtime_info())
#Runtime: .NET Framework
#=============
# Version:      <undefined>
# Initialized:  True
#  Shut down:    False
# Properties:
#   domain =
#   config_file = None
#

# I can add it as a reference. The printed description makes sense.
sdk = clr.AddReference("Suragus.Ec.Sdk")
print("SDK:", sdk)

# I can get its referenced assemblies. These are consistent with ILSpy.
from System.Reflection import Assembly
sdk_references = Assembly.GetReferencedAssemblies(sdk)
print("Referenced Assemblies:")
for item in sdk_references:
    print(item)

# Most the the referenced assemblies are printed here, but some are missing. The vendor asserts that they are not necessary.
print("ListAssemblies:")
for item in clr.ListAssemblies(True):
    print(item)

loaded_sdk = Assembly.Load("Suragus.Ec.Sdk")
print("Loaded:", loaded_sdk)

# But importing a namespace raises: "ModuleNotFoundError: No module named 'Suragus'".
import Suragus