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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"pdb: some expression results are printed to the debuggee stdout","articleBody":"# Bug report\n\n### Bug description:\n\nIn a dual-terminal / remote debugging setup, some expressions evaluated in pdb print their results to the debuggee’s stdout instead of the pdb output stream. For example, at the pdb prompt:\n- `(lambda: 123)()`\n- `sum(i for i in (1, 2, 3))`\n\ntheir results appear in the remote/debuggee terminal. I have screenshots and a minimal test case demonstrating the issue.\n\n**target.py**\n``` py\n# target.py\nimport os\nimport time\n\nprint(\"TARGET PID:\", os.getpid(), flush=True)\nprint(\"Target is running... waiting forever.\", flush=True)\n\nwhile True:\n    time.sleep(1)\n```\n\nattach.py\n``` py\n# attach.py\nimport sys\nimport pdb\n\npid = int(sys.argv[1])\nprint(\"Attaching to\", pid)\npdb.attach(pid)\n```\n\n\u003cimg width=\"2878\" height=\"1698\" alt=\"Image\" src=\"https://github.com/user-attachments/assets/7d67a793-e8e7-46a4-a722-895dd074a91b\" /\u003e\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nWindows\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-143875\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/hyongtao-code","@type":"Person","name":"hyongtao-code"},"datePublished":"2026-01-15T15:53:55.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/143874/cpython/issues/143874"}