Documents and Kernels

In the Jupyter architecture, kernels are separate processes started by the server that run your code in different programming languages and environments. JupyterLab enables you to connect any open text file to a {ref}code console and kernel <code-console>. This means you can easily run code from the text file in the kernel interactively.

(create-console)=

Right-click on a document and select “Create Console for Editor”:

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(send-code)=

Once the code console is open, send a single line of code or select a block of code and send it to the code console by hitting Shift Enter:

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(run-markdown)=

In a Markdown document, Shift Enter will automatically detect if the cursor is within a code block, and run the entire block if there is no selection:

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</div>

Any text file (Markdown, Python, R, LaTeX, C++, etc.) in a text file editor can be connected to a code console and kernel in this manner.

(subshell-console)=

Subshell Consoles

For kernels that support subshells (such as Python kernels with ipykernel 7.0.0+), you can create a subshell console to run code concurrently with the main notebook execution.

Creating a Subshell Console:

Command Palette: Press Ctrl+Shift+C (Cmd+Shift+C on Mac) and search for "New Subshell Console for Notebook"
Context Menu: Right-click in a notebook and select "New Subshell Console for Notebook" (only appears if kernel supports subshells)

Verifying Subshell Functionality:

Use the %subshell magic command in Python kernels:

python

%subshell

This displays:

subshell id: None for main shell, or a unique ID for subshells
subshell list: Array of active subshell IDs

Practical Example:

In your main notebook, start a long-running computation:

python

import time
for i in range(100):
    print(f"Main shell: {i}")
    time.sleep(1)

While this runs, create a subshell console and execute:

python

print("This runs concurrently!")
%subshell  # Shows this subshell's ID

The subshell executes immediately without waiting for the main shell to finish.

Communication Settings

Configure how widget communications use subshells via Settings → Advanced Settings → Kernel:

disabled: No subshells for communications
perCommTarget: One subshell per communication target (default)
perComm: One subshell per communication (can create many subshells)