Showing line numbers in IPython/Jupyter Notebooks

CTRL - ML toggles line numbers in the CodeMirror area. See the QuickHelp for other keyboard shortcuts.

In more details CTRL - M (or ESC) bring you to command mode, then pressing the L keys should toggle the visibility of current cell line numbers. In more recent notebook versions Shift-L should toggle for all cells.

If you can't remember the shortcut, bring up the command palette Ctrl-Shift+P (Cmd+Shift+P on Mac), and search for "line numbers"), it should allow to toggle and show you the shortcut.

On IPython 2.2.0, just typing l (lowercase L) on command mode (activated by typing Esc) works. See [Help] - [Keyboard Shortcuts] for other shortcuts.

Also, you can set default behavior to display line numbers by editing custom.js.

Select the Toggle Line Number Option from the View -> Toggle Line Number.

To turn line numbers on by default in all cells at startup I recommend this link. I quote:

1. Navigate to your jupyter config directory, which you can find by typing the following at the command line:

   jupyter --config-dir
   

2. From there, open or create the custom folder.

3. In that folder, you should find a custom.js file. If there isn’t one, you should be able to create one. Open it in a text editor and add this code:

   define([
       'base/js/namespace',
       'base/js/events'
       ],
       function(IPython, events) {
           events.on("app_initialized.NotebookApp",
               function () {
                   IPython.Cell.options_default.cm_config.lineNumbers = true;
               }
           );
       }
   );