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Switching frame will erase the local variable changes in pdb #102864
Description
This issue is related to #101673 , where f_locals being accessed during the debugging clears the changes of local variables. We need to only do one access of f_locals before giving back control.
def f():
a = 1
breakpoint()
print(a)
f()> /home/gaogaotiantian/programs/mycpython/example.py(4)f()
-> print(a)
(Pdb) p a
1
(Pdb) !a = 2
(Pdb) p a
2
(Pdb) u
> /home/gaogaotiantian/programs/mycpython/example.py(6)<module>()
-> f()
(Pdb) d
> /home/gaogaotiantian/programs/mycpython/example.py(4)f()
-> print(a)
(Pdb) p a
1
The worst part is, print_stack_entry calls format_stack_entry which is a bdb function, and it accesses f_locals. To keep the maximum compatibility of bdb, I decided to leave it alone and only fix pdb.
Activity
gaogaotiantian commentedon Mar 21, 2023
@iritkatriel could you take a look at the issue when you have some time as you reviewed the related one so you might already know the fundamental problem.
[-]Switching frame will erase the local variable changes[/-][+]Switching frame will erase the local variable changes in pdb[/+]iritkatriel commentedon Mar 21, 2023
When was this issue introduced? Is it part of the 3.10/3.11 changes to frames?
gaogaotiantian commentedon Mar 21, 2023
Unfortunately no. This issue has been there for a long time. As far as I can tell, you can repro it on 3.8. If I had to guess, it's probably when Python started using FAST instead of local variable dict.
gaogaotiantian commentedon May 5, 2024
This is fixed by PEP 667.
gh-102864: Add switching frame test for pdb (#119564)
pythongh-102864: Add switching frame test for pdb (python#119564)