How to reuse exsisting kernel?

[pplonski]

Hi!

I would like to create a kernel that can be reused between executions. For example I have two notebooks (each with only one code cell):

notebook-1.ipynb

a = 13

notebook-2.ipynb

print(a)

I would like to have one kernel that first will execute notebook-1.ipynb and then will execute notebook-2.ipynb.

What I'm currently trying:

import asyncio
from nbformat import read as nbread
from jupyter_client import AsyncKernelManager
from nbclient import execute

async def start():
    nb = nbread("notebook-1.ipynb", as_version=4)
    nb2 = nbread("notebook-2.ipynb", as_version=4)


    kernel_name = "python3"
    km = AsyncKernelManager(kernel_name=kernel_name)
    await km.start_kernel()

    # execute the notebook-1
    execute(nb, km=km)
    print(nb.cells)

    # execute the notebook-2
    execute(nb2, km=km)
    print(nb2.cells)


if __name__ == "__main__":
    asyncio.run(start())

I got an error:

raceback (most recent call last):
  File "kernel2.py", line 25, in <module>
    asyncio.run(start())
  File "/usr/lib/python3.8/asyncio/runners.py", line 43, in run
    return loop.run_until_complete(main)
  File "/usr/lib/python3.8/asyncio/base_events.py", line 608, in run_until_complete
    return future.result()
  File "kernel2.py", line 16, in start
    execute(nb, km=km)
  File "/home/piotr/sandbox/python-dashboard/pdenv/lib/python3.8/site-packages/nbclient/client.py", line 1204, in execute
    return NotebookClient(nb=nb, resources=resources, km=km, **kwargs).execute()
  File "/home/piotr/sandbox/python-dashboard/pdenv/lib/python3.8/site-packages/nbclient/util.py", line 84, in wrapped
    return just_run(coro(*args, **kwargs))
  File "/home/piotr/sandbox/python-dashboard/pdenv/lib/python3.8/site-packages/nbclient/util.py", line 62, in just_run
    return loop.run_until_complete(coro)
  File "/home/piotr/sandbox/python-dashboard/pdenv/lib/python3.8/site-packages/nest_asyncio.py", line 89, in run_until_complete
    return f.result()
  File "/usr/lib/python3.8/asyncio/futures.py", line 175, in result
    raise self._exception
  File "/usr/lib/python3.8/asyncio/tasks.py", line 280, in __step
    result = coro.send(None)
  File "/home/piotr/sandbox/python-dashboard/pdenv/lib/python3.8/site-packages/nbclient/client.py", line 648, in async_execute
    assert self.kc is not None
AssertionError

How to reuse existing kernel with nbclient?

[davidbrochart]

Thanks for reporting @pplonski.
I opened #239, it would be great if you could review it.

[pplonski]

@davidbrochart thanks for looking into this!

I've installed nbclient from your repo:

pip install -U git+https://github.com/davidbrochart/nbclient.git@main

and run the script and got the same error:

Traceback (most recent call last):
  File "kernel2.py", line 25, in <module>
    asyncio.run(start())
  File "/usr/lib/python3.8/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "/usr/lib/python3.8/asyncio/base_events.py", line 616, in run_until_complete
    return future.result()
  File "kernel2.py", line 16, in start
    execute(nb, km=km)
  File "/home/piotr/sandbox/python-dashboard/pdenv/lib/python3.8/site-packages/nbclient/client.py", line 1204, in execute
    return NotebookClient(nb=nb, resources=resources, km=km, **kwargs).execute()
  File "/home/piotr/sandbox/python-dashboard/pdenv/lib/python3.8/site-packages/nbclient/util.py", line 84, in wrapped
    return just_run(coro(*args, **kwargs))
  File "/home/piotr/sandbox/python-dashboard/pdenv/lib/python3.8/site-packages/nbclient/util.py", line 62, in just_run
    return loop.run_until_complete(coro)
  File "/home/piotr/sandbox/python-dashboard/pdenv/lib/python3.8/site-packages/nest_asyncio.py", line 89, in run_until_complete
    return f.result()
  File "/usr/lib/python3.8/asyncio/futures.py", line 178, in result
    raise self._exception
  File "/usr/lib/python3.8/asyncio/tasks.py", line 280, in __step
    result = coro.send(None)
  File "/home/piotr/sandbox/python-dashboard/pdenv/lib/python3.8/site-packages/nbclient/client.py", line 648, in async_execute
    assert self.kc is not None
AssertionError

is the additional check in the code in the correct place?

[davidbrochart]

You should install the fix_client branch:

pip install -U git+https://github.com/davidbrochart/nbclient.git@fix_client

[pplonski]

@davidbrochart thank you!

It is working! Thank you! :)