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Switching frame will erase the local variable changes in pdb #102864

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gaogaotiantian opened this issue Mar 21, 2023 · 4 comments
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Switching frame will erase the local variable changes in pdb #102864

gaogaotiantian opened this issue Mar 21, 2023 · 4 comments
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stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@gaogaotiantian
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gaogaotiantian commented Mar 21, 2023 •
edited by bedevere-app bot
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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.

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@gaogaotiantian gaogaotiantian added the type-bug An unexpected behavior, bug, or error label Mar 21, 2023
@bedevere-bot bedevere-bot mentioned this issue Mar 21, 2023
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@gaogaotiantian
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@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.

@gaogaotiantian gaogaotiantian changed the title Switching frame will erase the local variable changes Switching frame will erase the local variable changes in pdb Mar 21, 2023
@iritkatriel
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When was this issue introduced? Is it part of the 3.10/3.11 changes to frames?

@gaogaotiantian
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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.

@arhadthedev arhadthedev added the stdlib Python modules in the Lib dir label Mar 22, 2023
@gaogaotiantian gaogaotiantian mentioned this issue Apr 22, 2023
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@gaogaotiantian gaogaotiantian mentioned this issue Jun 3, 2023
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@gaogaotiantian
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This is fixed by PEP 667.

@bedevere-app bedevere-app bot mentioned this issue May 25, 2024
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iritkatriel pushed a commit that referenced this issue May 26, 2024
@gaogaotiantian
gh-102864: Add switching frame test for pdb (#119564)
5d04cc5
estyxx pushed a commit to estyxx/cpython that referenced this issue Jul 17, 2024
@gaogaotiantian @estyxx
pythongh-102864: Add switching frame test for pdb (python#119564)
a85ce6a
@gaogaotiantian gaogaotiantian mentioned this issue Sep 23, 2024
Merged
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