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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"pdb loses local variable change after command longlist","articleBody":"# Bug report\r\n\r\nIn pdb, `ll` will clear the local variable change.\r\n\r\n```python\r\ndef main():\r\n    a = 1\r\n    breakpoint()\r\n    print(a)\r\n\r\nmain()\r\n```\r\n\r\n```python\r\n-\u003e print(a)\r\n(Pdb) p a\r\n1\r\n(Pdb) !a = 2\r\n(Pdb) p a\r\n2\r\n(Pdb) ll\r\n  1     def main():\r\n  2         a = 1\r\n  3         breakpoint()\r\n  4  -\u003e     print(a)\r\n(Pdb) p a\r\n1\r\n(Pdb) s\r\n1\r\n--Return--\r\n```\r\n\r\nAs 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.\r\n\r\nThe 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.\r\n\r\n```python\r\nif inspect.isframe(obj) and obj.f_globals is obj.f_locals:\r\n```\r\n\r\nAs a result, the local variable changes will be erased.\r\n\r\nThe 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:\r\n\r\n```python\r\nif inspect.isframe(obj) and obj.f_code.co_name == \"\u003cmodule\u003e\":\r\n```\r\n\r\nIt might not be the most delicate way, but I can't think of a situation where this won't work.\r\n\r\nI did this change locally and I have confirmed:\r\n\r\n1. `./python -m test -j3` passed\r\n2. The original bug is fixed\r\n3. `ll` still prints the full file for module frame\r\n\r\nI'll make a PR soon and please let me know if there are any concerns about the fix.\r\n\r\n# Your environment\r\n\r\n- CPython versions tested on: 3.11.1\r\n- Operating system and architecture: Ubuntu 20.04\r\n\r\n\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-101674\n* gh-102632\n* gh-102633\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/gaogaotiantian","@type":"Person","name":"gaogaotiantian"},"datePublished":"2023-02-08T03:59:57.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/101673/cpython/issues/101673"}