Hangup when printing empty string to unbuffered stdout
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interpreter-core
OS-unsupported
topic-IO
type-bug
- Dominant language
- Python
- Stars
- 77.2k
- Forks
- 35.9k
- PR merge metrics
- PR metrics pending
Description
Crash report
What happened?
$ sudo python3 -u -c 'print(""); print("foo")'
Hangup
When printing an empty string to unbuffered stdout, under certain circumstances (e.g. when running on AIX under sudo, screen, tmux), the user session including the Python interpreter will terminate.
CPython versions tested on:
CPython main branch
Operating systems tested on:
Other
Output from running 'python -VV' on the command line:
Python 3.12.13 (main, Mar 6 2026, 03:56:12) [GCC 10.3.0]
Linked PRs
- gh-148774
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the reported command with unbuffered stdout, focusing on the AIX, sudo, screen, and tmux circumstances described in the issue. Review the linked PR gh-148774 and the relevant CPython stdout/write path it identifies. Done means the command no longer terminates the user session and the behavior is covered by an appropriate regression test.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- operating-systems
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 25/100