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Defining object members in Python

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#1

Hello everyone！
I want to define a NON-UPROPERY member in Python, which is not successful with various methods. My code is as follows:


import unreal
import ftrack_api


@unreal.uclass()
class FTrackProxyImplementation(unreal.FTrackProxy):

    @unreal.ufunction(override=True)
    def create_session(self, url, key, username):
        try:
            self.__session = ftrack_api.Session(server_url = url, api_key = key, api_user = username)
            print(self.__session)
            return True
        except Exception:  
            return False

    @unreal.ufunction(override=True)
    def close_session(self):
        unreal.log_warning("This is the Python test")
        print(self.__session)

The following error occurred in the console:


LogPython: <ftrack_api.session.Session object at 0x000001FA1202BC50>
LogSlate: Window 'Message' being destroyed
LogPython: Warning: This is the Python test
LogScript: Error: Script Msg: Traceback (most recent call last):
  File "D:/MyProjects/RTXProject/Plugins/FTrackBridge/Content/Python/FTrackProxy.py", line 24, in close_session
    print(self.__session)
AttributeError: 'FTrackProxyImplementation' object has no attribute '_FTrackProxyImplementation__session'
LogScript: Error: Script call stack:
    FTrackProxyImplementation.CloseSession

Obviously, the members of the object (self.__session) have been destroyed. Is there a solution for it?
Thanks!

#2

A Python object marked with uclass actually takes the Python definition, uses it to generate a UClass, and then re-writes the Python type to wrap that UClass.

As such it cannot reliably store data that isn’t in a UProperty, as only UProperties are added to the UClass and can be guaranteed to survive marshalling between the C++ instance and the Python wrapper.

If you do add data to the Python wrapper then it will survive only as long as the wrapper instance remains in scope.

#3

Thank you for your reply！Finally, I solved this problem by referring to a native Python object.
So, anthor question. Is the function which is a Python object method can not be invoked in the a thread?


class FLoginTask : public FNonAbandonableTask
{
    friend class FAutoDeleteAsyncTask<FLoginTask>;

public:
    FLoginTask(const FOnLogin& InOnLogin)
        :OnLogin(InOnLogin)
    {}

    FORCEINLINE TStatId GetStatId() const
    {
        RETURN_QUICK_DECLARE_CYCLE_STAT(FLoginTask, STATGROUP_ThreadPoolAsyncTasks);
    }
    void DoWork()
    {    
        UE_LOG(LogTemp, Warning, TEXT("FLoginTask DoWork0"));
        const UAssetManagerSettings* AssetManagerSettings = GetDefault<UAssetManagerSettings>();
        UFTrackProxy* Proxy = UFTrackProxy::Get();
        if (AssetManagerSettings && Proxy)
        {
            FString URL = AssetManagerSettings->URL;
            UE_LOG(LogTemp, Warning, TEXT("FLoginTask DoWork1"));
            bool Result = Proxy->Login(AssetManagerSettings->URL,
                AssetManagerSettings->ApiKey,
                AssetManagerSettings->UserName);    
            UE_LOG(LogTemp, Warning, TEXT("FLoginTask DoWork2"));
            OnLogin.Execute(Result);
            UE_LOG(LogTemp, Warning, TEXT("FLoginTask DoWork3"));        
    }
private:
    FOnLogin OnLogin;
};

Function “Proxy->Login()” will eventually call a method of a python object，It will only print the following information to the console:


LogTemp: Warning: FLoginTask DoWork0
LogTemp: Warning: FLoginTask DoWork1

Because the Python API is a blocking mode, I want to call it in the thread.
Thanks!