How do I block comment in Jupyter notebook? [closed]

Ctrl + / works for me in Chrome browser in MS Windows. On a Mac, use Cmd + / (thanks Anton K).

Please note, if / did not work out of the box, try pressing the / key on the Numpad. Credit: @DreamFlasher in comments to this question.

I have not yet managed to find the best way possible. Since I am using a keyboard with Finnish layout, some of the answers do not work for me (e.g. user5036413's answer).

However, in the meantime, I have come up with a solution that at least helps me not to comment each and every line one by one. I am using Chrome browser in MS Windows and I have not checked other possibilities though.

The solution:
It uses the fact that you can have multiple line cursors in an Ipython Notebook.

Press the Alt button and keep holding it. The cursor should change its shape into a big plus sign. The next step is, using your mouse, to point to the beginning of the first line you want to comment and while holding the Alt button pull down your mouse until the last line you want to comment. Finally, you can release the Alt button and then use the # character to comment. Voila! You have now commented multiple lines.

Try using the / from the numeric keyboard. Ctrl + / in Chrome wasn't working for me, but when I used the /(division symbol) from the numeric it worked.

Quick Addition to Top Answer: CTRL + / is nice because it toggles back and forth between adding and removing # at beginning of all selected lines. Didn't see that exact nuance mentioned so just wanted to add it here. (This worked in Firefox Developer Edition 54.0b12 on Windows 7).