Description

gaogaotiantian

opened on Feb 8, 2023

Issue body actions

Bug report

In pdb, ll will clear the local variable change.

def main():
    a = 1
    breakpoint()
    print(a)

main()

-> print(a)
(Pdb) p a
1
(Pdb) !a = 2
(Pdb) p a
2
(Pdb) ll
  1     def main():
  2         a = 1
  3         breakpoint()
  4  ->     print(a)
(Pdb) p a
1
(Pdb) s
1
--Return--

As you can tell, a was changed through !a = 2 but it was reverted after ll. print(a) also prints the unmodified value. Without ll, everything works fine.

The reason lies in getsourcelines in pdb.py. In that function, it tried to access obj.f_locals, which will refresh the dict with PyFrame_FastToLocalsWithError as it's a property now.

if inspect.isframe(obj) and obj.f_globals is obj.f_locals:

As a result, the local variable changes will be erased.

The original reason to check if obj.f_globals is obj.f_locals is to check whether obj is an module frame. Now that it has side effects to pdb, we can do the check with:

if inspect.isframe(obj) and obj.f_code.co_name == "<module>":

It might not be the most delicate way, but I can't think of a situation where this won't work.

I did this change locally and I have confirmed:

1. ./python -m test -j3 passed
2. The original bug is fixed
3. ll still prints the full file for module frame

I'll make a PR soon and please let me know if there are any concerns about the fix.

Your environment

• CPython versions tested on: 3.11.1
• Operating system and architecture: Ubuntu 20.04

Linked PRs

• GH-101673: Fix pdb bug that local variable changes lost after longlist #101674
• [3.11] GH-101673: Fix pdb bug where local variable changes are lost after longlist (GH-101674) #102632
• [3.10] GH-101673: Fix pdb bug where local variable changes are lost after longlist (#101674) #102633

Reacted by Oleg Iarygin, xpf629629, Travis, zyckk4, Harry, OysterMax, kelerensheng, Yao Xiao, Daniel Hahler and 3willows

Activity

1. gaogaotiantian

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Feb 8, 2023
2. gaogaotiantian commented on Mar 5, 2023

   

   gaogaotiantian

   on Mar 5, 2023

   MemberAuthor

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   Hi all, it's been about a month since this issue is created. I think this issue is pretty straightforward and easy to reproduce. The fix in #101674 is easy to understand and well contained. Could someone give this issue/PR a review? Thanks.
3. iritkatriel commented on Mar 11, 2023

   

   iritkatriel

   on Mar 11, 2023

   Member

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   Any bugfix PR should include a unit test to prevent regressions.
4. gaogaotiantian commented on Mar 12, 2023

   

   gaogaotiantian

   on Mar 12, 2023

   MemberAuthor

   More actions

   Hi @iritkatriel , thank you for the reminder! I've added the regression test for this bug - I confirmed that the test fails without the fix and passes with the fix.
5. iritkatriel

   added a commit that references this issue on Mar 12, 2023

   GH-101673: Fix pdb bug where local variable changes are lost after lo…

   5d677c5
6. miss-islington

   added a commit that references this issue on Mar 12, 2023

   pythonGH-101673: Fix pdb bug where local variable changes are lost af…

   bb6a288
7. iritkatriel

   added a commit that references this issue on Mar 12, 2023

   pythonGH-101673: Fix pdb bug where local variable changes are lost af…

   4e583c5
8. miss-islington

   added a commit that references this issue on Mar 12, 2023

   GH-101673: Fix pdb bug where local variable changes are lost after lo…

   7856026
9. pablogsal

   added a commit that references this issue on Mar 13, 2023

   [3.10] GH-101673: Fix pdb bug where local variable changes are lost a…

   d4f8faf
10. iritkatriel

    closed this as completedon Mar 13, 2023
11. warsaw

    added a commit that references this issue on Apr 11, 2023

    pythonGH-101673: Fix pdb bug where local variable changes are lost af…

    21858fd

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