Problem with stdOut

[Kiryuumaru]

Version

3.6.4

Details

Using linux. I have a python code that prints a string every seconds for 10 sconds. I want to read the output every seconds using this code:

await foreach (var cmdEvent in Cli.Wrap("python").WithArguments("test.py Joe").ListenAsync())
{
    switch (cmdEvent)
    {
        case StartedCommandEvent started:
            Console.WriteLine($"Process started; ID: {started.ProcessId}");
            break;
        case StandardOutputCommandEvent stdOut:
            Console.WriteLine($"Out> {stdOut.Text}");
            break;
        case StandardErrorCommandEvent stdErr:
            Console.WriteLine($"Err> {stdErr.Text}");
            break;
        case ExitedCommandEvent exited:
            Console.WriteLine($"Process exited; Code: {exited.ExitCode}");
            break;
    }
}

The python code test.py

import time
import sys

def print_hi(name):
    for _ in range(10):
        print(f'Hi, {name}')
        time.sleep(1)

if __name__ == '__main__':
    print_hi(sys.argv[0])

But this only prints everything after 10 seconds. Not every seconds. What might be the problem with this snippet.

Steps to reproduce

Use linux with python

[Tyrrrz]

I don't know how print works in Python, but do you need to flush the data by any chance?

[Kiryuumaru]

In python theres no need to flush when printing. This code will run normally when I execute it directly with python test.py "Joe". This will print every seconds Hi, Joe x10 .

[Tyrrrz]

Does print produce a newline at the end? ListenAsync() looks for line breaks.

[Kiryuumaru]

Yes. I also tried to manually add \n to the print

[Tyrrrz]

Not sure then

[Tyrrrz]

Could be related to #214

[Tyrrrz]

Were you able to work around this issue? Did you try using the raw Process class and see if it behaves differently with OutputDataReceived?

[WojciechNagorski]

Can you try to add -u attribute:

await foreach (var cmdEvent in Cli.Wrap("python").WithArguments("-u test.py Joe").ListenAsync())
{
    switch (cmdEvent)
    {
        case StartedCommandEvent started:
            Console.WriteLine($"Process started; ID: {started.ProcessId}");
            break;
        case StandardOutputCommandEvent stdOut:
            Console.WriteLine($"Out> {stdOut.Text}");
            break;
        case StandardErrorCommandEvent stdErr:
            Console.WriteLine($"Err> {stdErr.Text}");
            break;
        case ExitedCommandEvent exited:
            Console.WriteLine($"Process exited; Code: {exited.ExitCode}");
            break;
    }
}

Or set environment before: PYTHONUNBUFFERED=x

More info: -u forces the stdout and stderr streams to be unbuffered; this option has no effect on stdin; also PYTHONUNBUFFERED=x