How to show line numbers in Google Colaboratory?

Holding Ctrl and pressing ML (one by one) switches on/off line numbers in the cells containing code.

Yep, the shortcut (Ctrl + M + L) works,

other option is use the bar menu, at tool -> preference -> show line numbers

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Update: new path: Tools -> Settings -> Editor -> show line numbers

I see it under Tools->Settings->Editor (as on On 1//1/2020)