How to undo "Ignore errors like this"?

I can only comment from my Mac perspective but I could turn it off and back on again quite easily. For Windows it might be in the same place but I can't confirm that. What I did is:

1. Open the preferences or settings.

2. In the left-hand side, click Editor -> Code Style -> Inspections.

3. Select General in the middle pane.

4. There's a checkbox Line is longer than allowed by code style. Re-enable it.

Works for me but as I say, Windows PyCharm settings might be different.

Thanks! That's not exactly what I was looking for, but it pointed me in the right direction.This is how I ended up finding it:

1. Open the preferences or settings.
2. In the left-hand side, click Editor -> Code Style -> Inspections.
3. Select Python in the middle pane.
4. Highlight PEP 8 coding style violation in the list.
5. On the right pane is a box labeled Ignore errors, and errors to be ignored can be added or deleted from that box (in my case it was E501).

I have two machines, though, and unfortunately this process only fixed it on one of them. I'm still not getting some of the PEP8 inspections on the other. I'll have to write up a different question for that one. Thanks again!

For people that get here that don't know which inspection they just ignored, there's a helpful filter

1. Preferences
2. Editor -> Inspections
3. Next to the search above the list of inspections, there is a filter icon. In that menu there is Show Only Modified Inspections. Combined with the other filters, that should help find the inspection that you just accidentally ignored.