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GH-81881: Raise SpecialFileError for sockets and devices in shutil.copyfile#142693

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savannahostrowski merged 10 commits into
python:mainfrom
savannahostrowski:special-file-shutil
Jun 30, 2026
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GH-81881: Raise SpecialFileError for sockets and devices in shutil.copyfile#142693
savannahostrowski merged 10 commits into
python:mainfrom
savannahostrowski:special-file-shutil

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@savannahostrowski

@savannahostrowski savannahostrowski commented Dec 14, 2025 •
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The original issue just mentions sockets, but while documenting this I found it very confusing and inconsistent that device files didn't get the same treatment, so I figured I'd fix them all in one go.

📚 Documentation preview 📚: https://cpython-previews--142693.org.readthedocs.build/

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@savannahostrowski savannahostrowski marked this pull request as ready for review December 14, 2025 19:02
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This PR is stale because it has been open for 30 days with no activity.

@github-actions github-actions Bot added the stale Stale PR or inactive for long period of time. label May 3, 2026
@orsenthil

orsenthil commented Jun 27, 2026

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@savannahostrowski , are you interested in pursuing this. Overall this looks good to me.

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Documentation build overview

📚 cpython-previews | 🛠️ Build #33364327 | 📁 Comparing 78695f1 against main (46d1809)

  🔍 Preview build  

14 files changed · ± 14 modified

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@savannahostrowski

savannahostrowski commented Jun 29, 2026

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@orsenthil Yes, but was waiting for someone else to review it!

@orsenthil

orsenthil commented Jun 30, 2026

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Test failures in test_logging seems unrelated. It should be re-run.

  1. Raising for Socket devices is correct. The code raises OSError right now. So raising a specific sub-exception, SpecialFileError is correct.

  2. Block devices raise OSError too. So, good here.

For Character Device. This is a legitimate program at the moment and it will stop functioning after this change.

import shutil

shutil.copyfile('noisy_error_log.log', '/dev/null')
shutil.copyfile('/dev/null', 'empty_file.txt')

However, this is not pythonic and correct way piping to character device /dev/null is using subprocess.DEVNULL which uses os.devnull

Empty file is created using open and close call. Or pathlib.Path.touch

It only "works" because '/dev/null' happens to return EOF immediately It's incidental, not designed. Similarly, using /dev/random would be boundless call and an exploit.

So, it okay to raise against the Character Device too.

I did a github search of using shutil with /dev/null and I couldn't find any.

orsenthil
orsenthil approved these changes Jun 30, 2026
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LGTM

@orsenthil

orsenthil commented Jun 30, 2026

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but was waiting for someone else to review it!

Reviewed and approved. Thank you.

@savannahostrowski savannahostrowski enabled auto-merge (squash) June 30, 2026 19:41
@savannahostrowski savannahostrowski merged commit 040002c into python:main Jun 30, 2026
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maurycy added a commit to maurycy/cpython that referenced this pull request Jul 1, 2026
@maurycy
Merge branch 'main' into maurycy/bye-abba
da7d768 
* main: (266 commits)
  pythongh-151626: Fix tests that fail when PYTHONPYCACHEPREFIX is set (pythonGH-151952)
  pythongh-152728: IDLE - move 3 toplevel fix_xyz functions to idlelb.util (python#152729)
  pythongh-152711: Add pythoninfo-build command to Platforms/Android (python#152713)
  pythongh-152715: Add pythoninfo-build command to Platforms/Apple (python#152716)
  pythongh-152433: Windows: enable mmapmodule for UWP (python#152473)
  pythongh-152433: Windows: use GetFileSizeEx instead of GetFileSize for memory mapped files (python#152383)
  pythonGH-81881: Raise `SpecialFileError` for sockets and devices in `shutil.copyfile` (python#142693)
  pythongh-152502: Detect the curses mouse interface and is_* methods portably (pythonGH-152705)
  pythongh-145857: Replace `DELETE_GLOBAL` with `PUSH_NULL; STORE_GLOBAL` (pythonGH-146314)
  pythongh-145854: Replace `DELETE_NAME` with `PUSH_NULL; STORE_NAME` (pythonGH-146006)
  pythongh-152680: Detect container/VM in test.pythoninfo (python#152668)
  pythongh-152682: Fix NULL dereference on OOM in `symtable_visit_type_param_bound_or_default` (python#152684)
  pythongh-151881: Skip tk_inactive negativity check on Windows (pythonGH-152683)
  pythongh-152546: Refactor `mappingproxy.__new__` to use `PyDictProxy_New` (python#152547)
  pythongh-151126: Fix a possible crash during the startup with no memory under `Py_STACKREF_DEBUG` (python#152478)
  pythongh-152635: Raise MemoryError when the lock allocation fails in `_interpchannels.create()` (python#152642)
  pythongh-151029: Fix `test_remote_exec_deleted_static_executable` on static installed builds (pythonGH-152653)
  pythongh-121249: Deprecate using F/D type codes in the struct module (python#152309)
  pythongh-152192: Fix JUMP_BACKWARD passing a truncated oparg to the jit tracer (pythonGH-152382)
  Don't require the `_test{internal}capi` modules in `test_monitoring.py` (python#152311)
  ...
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@orsenthil orsenthil orsenthil approved these changes
@giampaolo giampaolo Awaiting requested review from giampaolo giampaolo is a code owner
@AA-Turner AA-Turner Awaiting requested review from AA-Turner AA-Turner is a code owner

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