python system_error ai_generated true

OSError: [Errno 9] Bad file descriptor During handling of the above exception, another exception occurred: ValueError: I/O operation on closed file

ID: python/pytest-capture-fd-error

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80%Fix Rate
82%Confidence
0Evidence
2024-08-27First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
7.x active — — —
8.x active — — —

Root Cause

A test closed sys.stdout/sys.stderr or a file descriptor that pytest's capture machinery (capfd/capsys) was using. This corrupts pytest's internal fd tracking.

generic

中文

某个测试关闭了 sys.stdout/sys.stderr 或 pytest 捕获机制（capfd/capsys）正在使用的文件描述符。这会破坏 pytest 内部的 fd 追踪。

Workarounds

  1. 92% success 
    Never close sys.stdout/sys.stderr in tests. If needed, use capsys:
  def test_x(capsys):
      out = capsys.readouterr().out
Or save/restore explicitly:
  saved = sys.stdout
  try: ...
  finally: sys.stdout = saved
  2. 88% success 
    For fd-level capture use capfd and avoid closing the underlying fd:
  def test_x(capfd):
      out, err = capfd.readouterr()

Dead Ends

Common approaches that don't work:

  1. 70% fail

    Hides the real bug: the test is still closing shared fds; other plugins may still fail.

  2. 80% fail

    The fd is already closed; subsequent capture operations still raise.