Hi all,
I have a weird case where I thought line events would be issued and yet
they aren't even though they're in the instructions in the bytecode (both
in 3.9 and 3.10).
i.e.:
Given the code:
def check_backtrack(x): # line 1
if not (x == 'a' # line 2
or x == 'c'): # line 3
pass # line 4
it has dis.dis such as:
2 0 LOAD_FAST 0 (x)
2 LOAD_CONST 1 ('a')
4 COMPARE_OP 2 (==)
6 POP_JUMP_IF_TRUE 12 (to 24)
3 8 LOAD_FAST 0 (x)
10 LOAD_CONST 2 ('c')
12 COMPARE_OP 2 (==)
2 14 POP_JUMP_IF_TRUE 10 (to 20)
4 16 LOAD_CONST 0 (None)
18 RETURN_VALUE
2 >> 20 LOAD_CONST 0 (None)
22 RETURN_VALUE
>> 24 LOAD_CONST 0 (None)
26 RETURN_VALUE
So, by just following the instructions/line numbers, I'd say that when the
instruction:
2 14 POP_JUMP_IF_TRUE 10 (to 20)
is executed, a line event would take place, yet, this isn't true, but if
that offset is changed to include more instructions then such a line event
is issued.
i.e.: something as:
def tracer(frame, event, arg):
print(frame, event)
return tracer
import sys
sys.settrace(tracer)
check_backtrack('f')
prints:
1 call
2 line
3 line
4 line
4 return
when I expected it to print:
1 call
2 line
3 line
2 line |<-- this is not being issued
4 line
4 return
So, I have some questions related to this:
Does anyone know why this happens?
What's the rule to identify this?
Why is that line number assigned to that instruction (i.e.: it seems a bit
odd that this is set up like that in the first place)?
Thanks,
Fabio
p.s.: I'm asking because in a debugger which changes bytecode I want to
keep the same semantics and it appears that if I add more bytecode at that
instruction offset, those semantics aren't kept (but I don't really know
what are the semantics to keep here since it seems like that instruction
should issue a line event even though it doesn't).
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