Hi everyone, Apologies for pinging the dev list; I'm shaving a very hairy yak, and the python-help crew, the docs, and the source are all unable to help.
Context: I'm working on a library function to dump stack traces for all threads, sorta like _Py_DumpTracebackThreads but in Python and meant to be invoked from a high layer, and thus be pretty and readable and so on rather than signal-safe and robust. The hard part is combining data from thread stack frames and exceptions, since people generally want to know about these. What I'm having trouble understanding is the relationship between an exception's TB and the thread's frame. Two important differences I've noticed are that (a) the output of traceback.print_tb(sys.exc_info()[2]) and traceback.print_stack(sys.exc_info()[2].tb_frame) are markedly different -- the former gives data about where the exception was raised, while the latter about where the thread currently is, usually in an exception handler and (b) if I'm in a unittest and dump the stack for a thread starting from its current frame (using traceback.format_stack and sys._current_frames), it gives a very deep stack that includes all the unittest harness code etc., but if I dump the stack for an exception starting from its TB object, it instead is very short and focused on where the exception happened. All of which tells me that I don't understand the relationship between the exception's traceback object and the frames it points to at all. Is there somewhere that explains this particular bit of magic, or someone who's well-versed in it? I have to admit that after a few hours of spelunking the code, I can't even figure out how the exception traceback is being set in the first place. :) Again, apologies for bugging the dev list with what (I hope) is a simple question -- if there's a FM I should be reading, please let me know! Yonatan
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