Writing the console output into a StringIO buffer from a thread (step-wise)

Question

I have a function that consist of a loop, from which I control the thread with semaphores:

import sys
from io import StringIO
import threading

# Create a semaphore object
sem = threading.Semaphore()

def my_function(event_set=True):
    # Start a loop
    for i in range(3):
        # Wait for the semaphore to be released
        sem.acquire()
        print("step", i)

        if event_set:
            sem.release()

# Create a new thread with the my_function function
t = threading.Thread(target=my_function, args=(False,))

After starting this thread, I can can print out each step, but I would like to store console output into a buffer. With the code below, I'm able to save 'step 0\nstep 1\nstep 2\n' in my_string after running the thread completely.

# Create a StringIO instance
embedder = StringIO()

# Set sys.stdout to the StringIO instance
previous_stdout = sys.stdout
sys.stdout = embedder

# Create a new thread with the my_function function
t = threading.Thread(target=my_function, args=(False,))

# Initialize
t.start()

# Process the thread sequentially
while t.is_alive():
    sem.release()

# Reset stdout
sys.stdout = previous_stdout

# Reset sys.stdout to its original value
my_string = embedder.getvalue()

However, I would like to save or read each step (i.e. 'step 0\n', then 'step 1\n', etc...) separately (and sequentially) right after calling sem.release() from my thread t. I have written something as follows:

# Process the thread sequentially
while t.is_alive():
    # Get the step string from buffer (after a thread .start() or .release())
    current_string = embedder.getvalue()

    # Reset the buffer
    embedder.seek(0)
    embedder.truncate(0)

    # Process next step of the function (which prints out a new step)
    sem.release()

When doig so, however, current_string does not capture the string of each step as 'step 0\n' or 'step 1\n' ... etc. Is there any way to so?