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Exception when deriving from a .NET class with abstract methods in Python #2571
Description
Environment
- Python.NET version: 3.0.5
- Tested on three configurations:
- Windows 10, Python 3.12.4, .NET Framework
- Windows 10, Python 3.12.4, .NET 9.0.201
- Debian 12, Python 3.11.2, .NET 8.0.407
Details
I have an abstract .NET class, which has abstract methods to override within a netstandard2.0 library. When I try to derive from such a class in Python, it throws a TypeError during class object creation.
Below is a basic example.
.NET library code:
namespace TestLib
{
public abstract class TestClass
{
public string Foo()
{
return "Foo";
}
protected abstract string Bar();
}
}Python code:
from pathlib import Path
import clr
clr.AddReference(str(Path(__file__).parent / 'TestLib.dll'))
from TestLib import TestClass
class SubTestClass(TestClass):
__namespace__ = 'CrlTest'
def Bar(self):
return 'Bar'
if __name__ == '__main__':
stc = SubTestClass()
print('Foo() -> ' + stc.Foo())
print('Bar() -> ' + stc.Bar())Python script output:
Traceback (most recent call last):
File "<redacted>\crl_test.py", line 10, in <module>
class SubTestClass(TestClass):
TypeError: Method 'Bar' in type 'CrlTest.SubTestClass' from assembly 'Python.Runtime.Dynamic, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' does not have an implementation.
Activity
Eswcvlad commentedon Apr 3, 2025
After some further testing, it looks like it is specifically the method being
protected abstract. If it ispublic abstract, as with an interface, then it works fine.Eswcvlad commentedon Apr 8, 2025
Looks like this is, actually, a duplicate of #2192, though having
protected abstractmethods makes the issue more annoying...For now I've forked it with a tweak to allow overriding protected methods. The downside is that all
protectedmethods get automatically wrapped intopublicones in Python, though, on the other hand, since Python doesn't differentiate between the two, it doesn't seem like a big deal...Make AbstractPdfDocumentEventHandler usable