.NET Intercepted STDOUT from Python is always empty in Unity

Question

I'm trying to use a Python program to send a continuous stream of information from one program to another, like this question, but in byte form.

pythonPath and pythonScript are just the file locations of the script and python.exe.

C# code

public static void PythonKernel_Test() {
    Process pythonProcess = Process.Start(new ProcessStartInfo() {
        FileName = pythonPath,
        Arguments = pythonScript,
        RedirectStandardOutput = true,
        RedirectStandardInput = true,
        UseShellExecute = false,
        CreateNoWindow = true
    });
    Stream pythonStdOut = pythonProcess.StandardOutput.BaseStream;
    for (int i = 0; i < 1000; i++) {
        byte[] buffer = new byte[256];
        pythonStdOut.Read(buffer, 0, 256);
        Debug.Log(Encoding.ASCII.GetString(buffer) + Environment.NewLine + BitConverter.ToString(buffer));
    }
    pythonStdOut.Close();
}

Although this is in Unity, you could just substitute Debug.Log for Console.WriteLine().

However, even though I am spamming stdout with SYNC, nothing appears on the C# side. It does however, appear in the command prompt when ran from shell.

Python code

w = sys.stdout.buffer
while True:
    w.write(b"SYNC\n")
    sys.stdout.flush()

I've been trying different IPC mechanisms that all incidentally use `write()` as their write functions, like pipes and sockets. — Timothy, Sep 22 '19 at 08:11

Sir Rufo · Accepted Answer · 2019-09-22T09:49:26.960

0

Here a working sample to try out

public static void PythonKernel_Test()
{
    var pi = new ProcessStartInfo
    {
        FileName = "python",
        Arguments = "test.py",
        RedirectStandardOutput = true,
        RedirectStandardError = true,
        CreateNoWindow = true,
    };
    var pythonProcess = new Process
    {
        StartInfo = pi,
    };

    pythonProcess.OutputDataReceived+= (s,e) => 
    {
        Console.WriteLine("OUT: {0}",e.Data);
    };
    pythonProcess.ErrorDataReceived+= (s,e) => 
    {
        Console.WriteLine("ERR: {0}",e.Data);
    };

    pythonProcess.Start();
    pythonProcess.BeginOutputReadLine();
    pythonProcess.BeginErrorReadLine();
    pythonProcess.WaitForExit();
}

It will read the output asynchronously

Taken from https://stackoverflow.com/a/29753402/1744164

test.py

import sys

while True:
    sys.stdout.write(b"SYNC\n")
    sys.stdout.flush()

edited Sep 22 '19 at 09:49

answered Sep 22 '19 at 08:40

Sir Rufo

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I'd like to do this synchronously if possible. – Timothy Sep 22 '19 at 08:44
Look at the link I gave you, there is an example for sync and async – Sir Rufo Sep 22 '19 at 08:45
Oh, so you're right. I didn't see it. Either way: Both methods return literally nothing. – Timothy Sep 22 '19 at 08:56
Well, a void method will return **void** which is in fact **nothing** – Sir Rufo Sep 22 '19 at 09:38
I meant `Read()`, `ReadLine()`, etc. are filling the buffers with nothing (and thus returning 0 always). Yeah I know the functions are void. – Timothy Sep 22 '19 at 09:41
1

I tested the above code and it was working as expected, I will add the python code too. Do you forgot the `import sys`? Without that line I only get an output on the Error output – Sir Rufo Sep 22 '19 at 09:48
Looks like it works outside of Unity, but not inside Unity itself. – Timothy Sep 22 '19 at 11:27

.NET Intercepted STDOUT from Python is always empty in Unity

C# code

Python code

1 Answers1