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Unable to modify C# List<T> #1153
Description
Environment
- Pythonnet version: 2.4.0
- Python version: 3.6
- Operating System: windows 10
Details
I have a C# class like this:
public class X
{
public List<string> list;
}I'm unable to do useful stuff with X.list due to the automatic value conversion of pythonnet.
Preface:
pylist=["a", "b", "c"]
x=X()
x.list=System.Collections.Generic.List[str]()Doesnt work:
x.list=System.Collections.Generic.List[str](pylist)Doesnt work:
for i in pylist:
x.list.Add(i)Doesnt work:
for i in pylist:
x.list.append(i)x.list is always empty except for the .Add call, with throws Exception cause the value is converted to python list. How do I modify a C# List in python?
Activity
filmor commentedon May 25, 2020
The
.Addcall works. What is the exact error you get there?jfu334 commentedon May 25, 2020
AttributeError: 'list' object has no attribute 'Add'
filmor commentedon May 25, 2020
And you are absolutely certain that
Xis indeed an object of your C# class?jfu334 commentedon May 25, 2020
Yes absolutely sure. I'd guess the detail here is that the List is retrieved through accessing the field of X.
jfu334 commentedon May 25, 2020
... confirmed. The code:
works. But not for x.list. So at least I have a workaround.
filmor commentedon May 25, 2020
Yes, you are right. There is some work going on to make these conversions optional. @lostmsu Could you chime in on how to exactly do that in this situation?
jfu334 commentedon May 25, 2020
Thanks for the fast response!
lostmsu commentedon May 26, 2020
@jfu334 sorry for late response. You should check out the new test for
RawProxyEncoder.Mind the
__namespace__element in the code class definition.koliyo commentedon Mar 8, 2021
So if I understand correctly, the #1122 pull request allows the workaround with the local list
l, but still not possible to callx.list.Add(...)Any update on if this should be expected to be fixed, or is the solution unknown for this use case?
lostmsu commentedon Mar 9, 2021
No, it should work in the
x.list.Add(...)scenario.richard-gemmell-42 commentedon Mar 30, 2021
First of all, I'd like to say that this project is awesome and I really appreciate the work that you've all put into it. Thanks.
The automatic conversion from IList'1 to a native python list causes another problem for us. There isn't a matching conversion from a native python list to an IList'1 so you can't 'round trip' a property value like this:
If x.List is declared to be of type IList rather than List then the behaviour is even more baffling. The value returned by x.List now depends on the type of the concrete object assigned to List and not the function prototype. If I assign a List to it then I get a python list back but if I assign a custom class which implements IList to it then I don't. This means that I can't tell the user what type of object to expect when the call x.List.
The design would be less surprising if:
I appreciate that it's probably difficult to change the design at this point but I thought I'd point it out.
In the mean time, I'm trying to use a RawProxyEncoder to disable the conversion from List. Unfortunately this triggers a stack overflow. Please see the link to issue #1427 above.
I wasn't sure these comments were worth another ticket so I thought I'd add them here. Please let me know if you think I should raise another ticket.
cheers,
Richard
lostmsu commentedon Mar 30, 2021
@richard-gemmell-42 I actually have a better design in my company's fork: when seen from Python .NET collection types have extra base classes (aka mixins), that implement Pythonic members using .NET members. See for example
https://github.com/losttech/pythonnet/blob/cae2d32729a35fb31f53fd694464f5c44392b896/src/runtime/Mixins/collections.py#L36
I am planning to upstream that feature before 3.0 is released.
lostmsu commentedon Sep 23, 2021
C# Lists are no longer automatically converted to Python
listin Python.NET 3.0, but still behave likelistdoes.