[FIXED] Jupyter Notebook cell run doesn't finalize

Issue

When I run Python code in the jupyter notebook, I got the following error, and cell doesn't finalize.

However, if I run the same Python code in the command line, it finishes its run without any problem.

[IPKernelApp] ERROR | Exception in message handler:
Traceback (most recent call last):
  File "/Users/burcakotlu/developer/python/test_venv/lib/python3.9/site-packages/ipykernel/kernelbase.py", line 424, in dispatch_shell
    await result
  File "/Users/burcakotlu/developer/python/test_venv/lib/python3.9/site-packages/ipykernel/kernelbase.py", line 770, in execute_request
    sys.stderr.flush()
ValueError: I/O operation on closed file.
[IPKernelApp] ERROR | Error in message handler
Traceback (most recent call last):
  File "/Users/burcakotlu/developer/python/test_venv/lib/python3.9/site-packages/ipykernel/kernelbase.py", line 529, in dispatch_queue
    await self.process_one()
  File "/Users/burcakotlu/developer/python/test_venv/lib/python3.9/site-packages/ipykernel/kernelbase.py", line 518, in process_one
    await dispatch(*args)
  File "/Users/burcakotlu/developer/python/test_venv/lib/python3.9/site-packages/ipykernel/kernelbase.py", line 437, in dispatch_shell
    sys.stderr.flush()
ValueError: I/O operation on closed file.

I haven't solved this issue for days. I would appreciate any help.

Env specific versions:

$ pip list | grep -E "(^jup|^ipy)"
ipykernel                  6.27.1
ipython                    8.18.1
jupyter_client             8.6.0
jupyter_core               5.5.0

Solution

Thanks for your help. Comments from @julaine writing that the server can't flush stderr, which is very unusual wake me up.

I remembered that somewhere in my code I have done the following.

sys.stderr = open(error_file, 'w')
...
...
...
sys.stderr.close()

So I had redirected the sys.stderr to a file and then closed it. Then I got the following error

sys.stderr.flush()
ValueError: I/O operation on closed file.

Changing the code as follows solved the issue:

temp = sys.stderr 
sys.stderr = open(error_file, 'w')
...
...
...
sys.stderr.close()
sys.stderr = temp 

Redirecting sys.stderr to what it was pointing before resolved the problem.

There is even a better solution without using a temporary variable.

sys.stderr = open(error_file, 'w')
...
...
...
sys.stderr.close()
sys.stderr = sys.__stderr__ 

Answered By - burcak