redirect sys.stdout to specific Jupyter Notebook cell

The documentation for ipywidgets.Output has a section about interacting with output widgets from background threads. Using the Output.append_stdout method there is no need for locking. The final cell in this answer can then be replaced with:

def t1_main():    for i in range(10):        output1.append_stdout(f'thread1 {i}\n')        time.sleep(0.5)def t2_main():    for i in range(10):        output2.append_stdout(f'thread2 {i}\n')        time.sleep(0.5)output1.clear_output()output2.clear_output()        t1 = Thread(target=t1_main)t2 = Thread(target=t2_main)t1.start()t2.start()t1.join()t2.join()

You can use a combination of ipywidgets.Output (docs) and locking:

Code in jupyter cells:

# In[1]:from threading import Thread, Lockimport timefrom ipywidgets import Output# In[2]:output1 = Output()output1# In[3]:output2 = Output()output2# In[4]:print_lock = Lock()def t1_main():        for i in range(10):        with print_lock, output1:            print('thread1', i)        time.sleep(0.5)def t2_main():    for i in range(10):        with print_lock, output2:            print('thread2', i)        time.sleep(0.5)output1.clear_output()output2.clear_output()        t1 = Thread(target=t1_main)t2 = Thread(target=t2_main)t1.start()t2.start()t1.join()t2.join()