Keystroke to return focus to the code pane.

Example: I am coding away and shift focus in the Project browser (⌘1) to look at something or other. Or run something (⌘4). How do I quickly shift back to where I was in the code? A quick tap on ^tab moves focus to the next file in the stack (aaaagh!)

This is driving me bonkers. I understand that ^tab can eventually return focus to the current code window but is there a single keystroke that can do the same?

It seems that there's a keystroke for everything but this!

(Mac Pycharm, vim keystrokes installed)