KeyError when running self.mpl_modules_for_patching.pop(module)

[brettcannon]

microsoft/vscode-python#2982

I'm guessing there's a race condition, in which case this probably just needs a try/except KeyError: pass block to avoid this issue.

[stefan--]

please see microsoft/vscode-python#2982 (comment) for replication instructions.

[yzhang-gh]

Here I get one more warning before the error

WARNING: QApplication was not created in the main() thread.  <- **This line**
Backend Qt5Agg is interactive backend. Turning interactive mode on.
Traceback (most recent call last):

  ... (the same)

KeyError: 'matplotlib.pyplot'

[fabioz]

Just provided a fix where the initialization/event loop will only take place in the main thread (processing the event loop out of the main thread is an error and this prevents the racing condition too).

[karthiknadig]

Fixed via #1121