GeezerVison

Ignoring all warnings was intentional. Compile also issues DeprecationWarnings. Narrowing the filter to SyntaxWarning only reintroduces the error of DeprecationWarning being issued thrice, which was fixed by the previous code. I will write more on the issue.

Followup PR fixes regression by removing SyntaxWarning.

Then maybe the catch warnings need to be put in there 3 times, to reset the warning filter on each subsequent compilations ?

This source should not have '\n' as single lines are passed without it. That is why to recompile with \n and \n\n added. Fixed in followup PR.

Even w/o the \n 3.8.5 does not raise the SyntaxError.

$ cat foo.py
import warnings
from codeop import compile_command

warnings.simplefilter('error', SyntaxWarning)
res = compile_command('1 is 1', symbol='exec')
print('Res', res)

$ python foo.py
Res None

I expect that, but aside from your issue, the test if better if it calls compile_command the way it is intended to be used and is used by code.InteractiveInterpreter.