Show code line numbers in JupyterLab

You can go to View -> Show Line Numbers:

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which will display line numbers in the notebook:

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you can turn this on by default by going into Settings --> Advanced Settings Editor:

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As you can see from the screenshot, you can edit other features as well and easily set them back to default by deleting your 'User Overrides'

Go to Settings > Advanced configuration and add:

{
    "codeCellConfig": {
        "lineNumbers": true
    }
}

Late reply, but it'll still help others!

For Windows users, just hit Shift + L

https://github.com/jupyterlab/jupyterlab/issues/2395 - Shift+L toggles line number visibility.

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