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
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