Log output of multiprocessing.Process

Here is the simple and straightforward way for capturing stdout for multiprocessing.Process and io.TextIOWrapper:

import app
import io
import sys
from multiprocessing import Process


def run_app(some_param):
    out_file = open(sys.stdout.fileno(), 'wb', 0)
    sys.stdout = io.TextIOWrapper(out_file, write_through=True)
    app.run()

app_process = Process(target=run_app, args=('some_param',))
app_process.start()
# Use app_process.termninate() for python <= 3.7.
app_process.kill() 

The log_to_stderr() function is the simplest solution.

From PYMOTW:

multiprocessing has a convenient module-level function to enable logging called log_to_stderr(). It sets up a logger object using logging and adds a handler so that log messages are sent to the standard error channel. By default, the logging level is set to NOTSET so no messages are produced. Pass a different level to initialize the logger to the level of detail desired.

import logging
from multiprocessing import Process, log_to_stderr

print("Running main script...")

def my_process(my_var):
    print(f"Running my_process with {my_var}...")

# Initialize logging for multiprocessing.
log_to_stderr(logging.DEBUG)

# Start the process.
my_var = 100;
process = Process(target=my_process, args=(my_var,))
process.start()
process.kill()

This code will output both print() statements to stderr.