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.