With PEP-415 accepted as the implementation of the "raise exc from None" syntax, it raises the prospect of exceptions with both __cause__ and __context__ set to non-None values, and __suppress_context__ set to False.

The initial PEP-415 patch treats this case the same way PEP-409 did: it ignores __context__ if *either* __cause__ is not None *or* __suppress_context__ is True.

This issue proposes that at least the default exception display routine and the display routine in the traceback module be updated to display the __context__ any time __suppress_context__ is False, even if __cause__ is also non-None.

And don't forget about print_exception() in Lib/idlelib/run.py.

and the code module (after bpo-17442 is resolved)

@gvanrossum says says that the current behaviour is by design, and this ticket should be closed.

I asked why the design is intended (since neither the PEP nor the documentation explains) and Guido says I should ask it here.

I suppose the reason is that if you take both cause and context into account, you end up with a tree -- each cause may itself have another cause and another context, and ditto for each context. Displaying such a tree (where each node is a traceback that could be many stack frames deep) would be complicated, and probably produce more confusion than understanding in most users. Plus, because cause is set explicitly while context is implicit, it stands to reason that when the failing code indicates a context, the cause is not important enough to display.