SystemError: error return without exception set

[Elizaveta239]

Hi, Fabio!

I'm currently merging latest changes from PyDev to PyCharm, thank you very much for all the new features and fixes added. Unfortunately at the moment I'm getting the following error twice when stopping at line breakpoint:

Exception ignored in: <generator object WeakSet.__iter__ at 0x10dce8a98>
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/_weakrefset.py", line 65, in __iter__
    yield item
SystemError: error return without exception set

I figured out that the problem appeared after this commit: https://github.com/fabioz/PyDev.Debugger/commit/77819b14274814d865bac2f4debd09726bc3942e

Before diving into debugging I want to ask if you faced anything similar in PyDev or VSCode? Do you have any ideas why it can appear?

[fabioz]

Hi Elizaveta,

I'm not currently experiencing this issue, so, I went to investigate a bit on why you may have that and found out that I can reproduce it by turning on the frame evaluation mode and running all tests -- you can see that pydevd_frame_eval_main.py has PYDEVD_USE_FRAME_EVAL set to NO by default now.

The main reason for disabling it is that there was a serious performance regression if the user changed breakpoints with that mode turned on (the debugger was much much slower than even a regular always tracing on debugger -- see: https://github.com/Microsoft/ptvsd/issues/358#issuecomment-390966462 for more info).

The plan is re-enabling this mode later on, but it needs work (so, it seems that besides that initial problem some other regression has been added due to other changes -- my guess is that this is close to the other issue where the frame eval mode and tracing mode are conflicting somehow).

I'm not sure the best approach now -- I'd suggest disabling that mode on PyCharm too until the related issues are resolved (which is the same approach PyDev/VSCode took) and re-enabling after those are fixed (i.e.: this is already planned but there are some other issues I have planned to take a look before this one).

[Elizaveta239]

@fabioz Thank you!