Showing line numbers in IPython/Jupyter Notebooks

Error reports from most language kernels running in IPython/Jupyter Notebooks indicate the line on which the error occurred; but (at least by default) no line numbers are indicated in Notebooks.

Is it possibile to add the line numbers to 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.

The menu looks like this

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

Navigate to your jupyter config directory, which you can find by typing the following at the command line:
jupyter --config-dir
From there, open or create the custom folder.
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;
            }
        );
    }
);