Hi Denis,
Thanks for your fast response. Sounds completely reasonable to me. And this has not been too much of an issue for me.
I got rid of the abstract base class simply by providing an “empty” implementation and using a non-abstract base class. No need for meta classes any more. This way, I got rid of error messages. Great!
Unfortunately, there seem to be an issue when calling a virtual method inside the C# implementation. Even when overriding this virtual method in Python, it’s still the base class’ implementation which is called.
See the new simple base class defined in C#:
namespace PythonBaseClass
{
using System;
public class Door
{
public virtual void Open()
{
if (!IsOpen())
Toggle();
}
public virtual void Close()
{
if (IsOpen())
Toggle();
}
public virtual bool IsOpen()
{
Console.WriteLine("Door.
IsOpen()" );return false;
}
public virtual void Toggle()
{
Console.WriteLine("Door.
Toggle()" );}
}
}
The consuming Python code now looks like this:
import clr
from PythonBaseClass import Door
class StringDoor(Door):
def __init__(self):
self.status = "closed"
def IsOpen(self):
print "StringDoor.IsOpen()"
return self.status == "open"
def Toggle(self):
print "StringDoor.Toggle()"
if self.status == "open":
self.status = "closed"
else:
self.status = "open"
But the output does not look like expected:
Python 2.7.12 (v2.7.12:d33e0cf91556, Jun 27 2016, 15:19:22) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from PythonInheritedClass import StringDoor
>>> d = StringDoor()
>>> d.status
'closed'
>>> d.Open()
Door.IsOpen()
Door.Toggle()
>>> d.status
'closed'
>>>
From my understanding, the output should rather read “StringDoor.<something>()” instead of “Door.<something>()”. Obviously, only the base implementation is called but the overridden methods are ignored.
Also a limitation of inheriting C# classes in pythonnet?
BR,
Henning
From: PythonDotNet [mailto:pythondotnet-bounces+
hmoeller =comprion.com@python.org ] On Behalf Of Denis Akhiyarov
Sent: Donnerstag, 22. September 2016 19:38
To: A list for users and developers of Python for .NET <pythondotnet@python.org>
Subject: Re: [Python.NET] Inheriting from abstract .NET class
You are not a "Python n00b" based on metaclass usage!
My recommendation is to keep simple integration layer between CPython and .NET, hence metaclasses were/are not supported.
But contributions are welcome! Although I expect this to be a tremendous undertaking based on reviewing multiple sources.
Note that metaclass is a very different low-level concept from higher-level abstract classes in .NET, hence direct mapping (e.g. `.register()` ) is not feasible.
Thanks,
Denis
On Thu, Sep 22, 2016 at 10:04 AM, Henning Moeller <HMoeller@comprion.com> wrote:
Hello out there,
I’m trying to inherit from an abstract .NET base class in Python (2.7). I’m a Python n00b but from what I understood…
Here’s what I managed to do in Python only and which works fine:
[File: room.py] -------
import abc
class Room(object):
def __init__(self, door):
self.door = door
def open(self):
self.door.open()
def close(self):
self.door.close()
def is_open(self):
return self.door.is_open()
class Door(object):
__metaclass__ = abc.ABCMeta
def open(self):
if not self.is_open():
self.toggle()
def close(self):
if self.is_open():
self.toggle()
@abc.abstractmethod
def is_open(self):
pass
@abc.abstractmethod
def toggle(self):
pass
class StringDoor(Door):
def __init__(self):
self.status = "closed"
def is_open(self):
return self.status == "open"
def toggle(self):
if self.status == "open":
self.status = "closed"
else:
self.status = "open"
class BooleanDoor(Door):
def __init__(self):
self.status = True
def is_open(self):
return self.status
def toggle(self):
self.status = not (self.status)
Door.register(StringDoor)
Door.register(BooleanDoor)
-------
Now, all I did was to replace the abstract base class Door by a C# representation:
[File: PythonAbstractBaseClass.dll] -------
namespace PythonAbstractBaseClass
{
public abstract class Door
{
public virtual void Open()
{
if (!IsOpen())
Toggle();
}
public virtual void Close()
{
if (IsOpen())
Toggle();
}
public abstract bool IsOpen();
public abstract void Toggle();
}
}
-------
Removing Door from the Python part and importing it from the .NET assembly instead, I end up with this:
[File: room2.py] -------
import clr
import abc
from PythonAbstractBaseClass import Door
class Room(object):
def __init__(self, door):
self.door = door
def open(self):
self.door.open()
def close(self):
self.door.close()
def is_open(self):
return self.door.is_open()
class StringDoor(Door):
def __init__(self):
self.status = "closed"
def is_open(self):
return self.status == "open"
def toggle(self):
if self.status == "open":
self.status = "closed"
else:
self.status = "open"
class BooleanDoor(Door):
def __init__(self):
self.status = True
def is_open(self):
return self.status
def toggle(self):
self.status = not (self.status)
Door.register(StringDoor)
Door.register(BooleanDoor)
-------
But this fails with the following error message:
Door.register(StringDoor)
AttributeError: type object 'Door' has no attribute 'register'
From what I understood about abc.ABCMeta, this metaclass contributes the ‘register’ method. It seems that abstract C# classes do not come with the same metaclass. They instead come with metaclass “CLR Metatype” which obviously does not provide ‘register’.
But if I drop the call to ‘register’, on instantiating one of the derived classes, I receive the error message
sdoor = StringDoor()
TypeError: cannot instantiate abstract class
Is there a way to inherit from an abstract .NET class or is this is missing feature?
Thanks in advance,
Henning
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