Python: Start process. Keep StdOut and StdErr in the original order. Display output real time character by character. Capture output on exit.

popen.py

#!/usr/bin/python3
# -*- coding: utf-8 -*-

# Requirements:
# Python 3.7+ (uses data classes, lines 16 and 25).

import dataclasses as dc
import os
import subprocess
import sys
import traceback
from collections.abc import Sequence
from typing import TextIO, Union


@dc.dataclass()
class ProcessOptions:
    command: Sequence[str]
    wait: bool = True
    shell: bool = False
    new_console: bool = False
    hide: bool = False


@dc.dataclass()
class ProcessResult:
    exit_code: int = -1
    output: str = ''


class App:

    @staticmethod
    def start_process(opts: ProcessOptions) -> ProcessResult:
        result: ProcessResult = ProcessResult()

        startup_info: subprocess.STARTUPINFO = subprocess.STARTUPINFO()
        creation_flags: int = 0

        std_out: Union[int, TextIO, None] = None
        std_err: Union[int, TextIO, None] = None
        std_in: Union[int, TextIO, None] = None

        if opts.new_console or opts.hide:
            if opts.new_console:
                creation_flags |= subprocess.CREATE_NEW_CONSOLE
            if opts.hide:
                startup_info.dwFlags |= subprocess.STARTF_USESHOWWINDOW
        else:  # Can capture output...
            std_out = subprocess.PIPE
            std_err = subprocess.STDOUT
            # Fix "ERROR: Input redirection is not supported, exiting the process immediately" on Windows:
            std_in = sys.stdin

        proc: subprocess.Popen[str] = subprocess.Popen(
            opts.command,
            encoding='utf-8',
            shell=opts.shell,
            startupinfo=startup_info,
            creationflags=creation_flags,
            stdout=std_out,
            stderr=std_err,
            stdin=std_in,
        )

        can_capture_out: bool = not opts.new_console and not opts.hide

        if can_capture_out and opts.wait:
            while True:
                char = proc.stdout.read(1)
                if char == '' and proc.poll() is not None:
                    break
                if char:
                    result.output += char
                    sys.stdout.write(char)
                    sys.stdout.flush()

        if opts.wait:
            proc.wait()

        result.exit_code = proc.poll()

        return result

    @staticmethod
    def main() -> None:
        opts: ProcessOptions = ProcessOptions(
            command=('my-executable-name', 'arg1'),
            wait=True,
            # shell=False,
            # new_console=False,
            # hide=False,
        )

        result: ProcessResult = App.start_process(opts)

        print('-' * 30)
        print(result.output)
        print('Exit code:', result.exit_code)
        input('Press <Enter> to exit...\n')


# Main start point.
if __name__ == '__main__':
    # noinspection PyBroadException
    try:
        os.chdir(sys.path[0])

        App.main()
    except Exception:
        traceback.print_exc()

        input('Press <Enter> to exit...\n')

        exit(1)