SetOutput to stream doesn't work (3.4.0-alpha1)

[DJSures]

Description

We're attempting to capture the output to a stream. It is never called.

*Note: This used to work in the Iron Python 2 version - we're using the same codebase.

Steps to Reproduce

This example will demonstrate how the stdout isn't being captured by the stream assignment. The iron python script is running in a thread in a loop printing to the stdout. The assignment to the SetOutput stream is set but the stream is never written to.

     public class StreamWriteEvent : MemoryStream {

      public event EventHandler<string> OnNewText;

      public override void Write(byte[] buffer, int offset, int count) {

        OnNewText?.Invoke(this, Encoding.Default.GetString(buffer, offset, count));

        base.Write(buffer, offset, count);
      }

      public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken) {

        OnNewText?.Invoke(this, Encoding.Default.GetString(buffer, offset, count));

        return base.WriteAsync(buffer, offset, count, cancellationToken);
      }

      public override void WriteByte(byte value) {

        OnNewText?.Invoke(this, value.ToString());

        base.WriteByte(value);
      }

      public override IAsyncResult BeginWrite(byte[] buffer, int offset, int count, AsyncCallback callback, object state) {

        OnNewText?.Invoke(this, Encoding.Default.GetString(buffer, offset, count));

        return base.BeginWrite(buffer, offset, count, callback, state);
      }
    }

    ScriptEngine _engine;
    ScriptScope _scope;

    // Run a python script in a new thread
    private void button2_Click(object sender, EventArgs e) {

      Thread ts = new Thread(runScript);
      ts.Start();
    }

    // This thread is running the python script
    void runScript() {

      var streamWriter = new StreamWriteEvent();
      streamWriter.OnNewText += StreamWriter_OnNewText;

      _engine = IronPython.Hosting.Python.CreateEngine();

      _engine.Runtime.IO.SetErrorOutput(streamWriter, Encoding.ASCII);
      _engine.Runtime.IO.SetOutput(streamWriter, Encoding.ASCII);

      _scope = _engine.CreateScope();

      // Run a script that loops
      // We will test both capturing the output stream & the Shutdown command to stop the running script
      var sc = _engine.CreateScriptSourceFromString(@"
while True:
  print('This should output something')
");

      var ret = sc.Execute(_scope);

      // This doesn't do anything. It doesn't stop the running script.
      Console.WriteLine("Shut down");
    }

    private void StreamWriter_OnNewText(object sender, string e) {

      // This should output but never does
      Console.WriteLine("From steam writer" + e);
    }

    // This is the button that should stop the running python script
    private void button3_Click(object sender, EventArgs e) {

      Console.WriteLine("Shutting down...");

      // This shutdown command doesn't work. The script will continue running.
      _scope.Engine.Runtime.Shutdown();
    }

Expected behavior: The stream contains the output of the print() statement

Actual behavior: No output from print() statements in the stream

Versions

3.4.0-alpha1 for .Net Framework 4.7.2 from nuget

[slozier]

This is probably the same as https://github.com/IronLanguages/ironpython3/issues/961. A potential workaround is noted in that issue:

var runtime = IronPython.Hosting.Python.CreateRuntime();

runtime.IO.SetErrorOutput(streamWriter, Encoding.ASCII);
runtime.IO.SetOutput(streamWriter, Encoding.ASCII);

_engine = IronPython.Hosting.Python.GetEngine(runtime);

[DJSures]

Thank you - that works. It's a strange workaround but it works :D

[zhanglongtumi]

Thank you - that works. NB

[KanaHayama]

Hi, I am using IronPython 3.4.0 and having a same problem. I am trying to redirect outputs to std IO. The default behavior does not work. So, I tried to redirect it explicitly, but it still doesn't work. Then I found this github issue and wanted to try the workaround. But there is not an overload of SetOutput() that taking TextWriter as its first parameter. Is it removed?

[slozier]

@KanaHayama There is no overload with TextWriter as the first parameter, the streamWriter in the workaround is a Stream. If you need to use a TextWriter you can try wrapping it as described in the documentation on redirecting output.