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Calling overridden method with out parameter from C# to python results in 0xC0000005 (Access Violation) #1481
Description
Environment
- Pythonnet version: 2.5.2
- Python version: 3.8.3
- Operating System: Win10 64bit
- .NET Runtime: 4.8
Details
- Describe what you were trying to get done.
In C# I have defined an interface with a method with an out parameter. I implemented this interface in python, an now I want to call this method from C#. (using pythonnet)
What I see is that a method without out parameter works fine, but a method with an out parameter throws an access violation.
I know that out parameters are handled differently in pythonnet: you return a tuple with first the return value and the second tuple item is the out parameter.
- What commands did you run to trigger this issue? If you can provide a
Minimal, Complete, and Verifiable example
this will help us understand the issue.
My C# code
public interface IMyInterface
{
string MyMethod_Out(string name, out int index);
string MyMethod(string name);
}
public class MyServer
{
public void CallMyMethod_Out(IMyInterface myInterface)
{
Console.WriteLine("C#.CallMyMethod_Out: before MyMethod_Out");
int index = 1;
myInterface.MyMethod_Out("myclient", out index);
Console.WriteLine($"C#:CallMyMethod_Out: after MyMethod_Out: index:{index}");
}
public void CallMyMethod(IMyInterface myInterface)
{
Console.WriteLine("C#.CallMyMethod: before MyMethod");
myInterface.MyMethod("myclient");
Console.WriteLine($"C#:CallMyMethod: after MyMethod");
}
public void DoSomething()
{
Console.WriteLine("C#.DoSomething");
}
}My Python code:
import clr
import sys
sys.path.append('some_dir')
clr.AddReference("ClassLibrary1")
from ClassLibrary1 import IMyInterface, MyServer
class MyInterfaceImpl(IMyInterface):
__namespace__ = "ClassLibrary1"
def MyMethod_Out(self, name, index):
print("Python.MyInterfaceImpl.MyMethod_Out")
other_index = 101
return ('MyName', other_index)
def MyMethod(self, name):
print("Python.MyInterfaceImpl.MyMethod")
return 'MyName'
print('\nCall regular C# function')
my_server = MyServer()
my_server.DoSomething()
my_interface_impl = MyInterfaceImpl()
print('\nCall without out param')
my_server.CallMyMethod(my_interface_impl)
print('\nCall with out param')
my_server.CallMyMethod_Out(my_interface_impl) # Access Violation 0xC0000005- If there was a crash, please include the traceback here.
Output:
Call regular C# function
C#.DoSomethingCall without out param
C#.CallMyMethod: before MyMethod
Python.MyInterfaceImpl.MyMethod
C#:CallMyMethod: after MyMethodCall with out param
C#.CallMyMethod_Out: before MyMethod_Out
Process finished with exit code -1073741819 (0xC0000005)
Expected output
...
Call with out param
C#.CallMyMethod_Out: before MyMethod_Out
Python.MyInterfaceImpl.MyMethod_Out
C#:CallMyMethod_Out: after MyMethod_Out: index:101
Activity
filmor commentedon Jul 6, 2021
Can you please test this with the current
master? I vaguely remember a similar issue that has been fixed a while ago.roy-van-de-korput commentedon Jul 6, 2021
I just retried with master (ea61b03) . Same error.
default-writer commentedon Dec 4, 2021
You are not just override method, you are returning Tuple instead of a String, what whould you expect for that?
return type String:
string MyMethod_Out(string name, out int index);
return type Tuple<String,Int>
return ('MyName', other_index)
lostmsu commentedon Jan 6, 2022
This is a very involved issue, that requires dynamic code generation to be rewritten to support byref arguments. For now unless somebody wants to pick it up, I suggest we document it and move along.
As a workaround one can define another interface in .NET that does not have
outorrefparameters, and a class serving as an adapter between the original interface and the new one.added support for byref parameters when overriding .NET methods from …
added support for byref parameters when overriding .NET methods from …
added support for byref parameters when overriding .NET methods from …
added support for byref parameters when overriding .NET methods from …
lostmsu commentedon Jan 6, 2022
😁 I got bored and made #1663
added support for byref parameters when overriding .NET methods from …
added support for byref parameters when overriding .NET methods from …