What did you do?

After upgrading one of our Django projects to Pillow 8.3.0 we got a 500 error when trying to create a thumbnail on any page. Downgrading to Pillow 8.2.0 resolved (worked around) the error.

What did you expect to happen?

Image resizing to continue as normal.

What actually happened?

A 500 error and a long backtrace in the logs:

Internal Server Error: /case-studies/chronic-pelvic-pain/
Traceback (most recent call last):
    ...
    File "...lib/python3.8/site-packages/PIL/ImageFile.py", line 496, in _save
        if fp == sys.stdout or (hasattr(sys.stdout, "buffer") and fp == sys.stdout.buffer):
    OSError: sys.stdout access restricted by mod_wsgi

What are your OS, Python and Pillow versions?

• OS: Ubuntu 20.04.2 LTS (Linux 5.8.0-1038-aws)
• Python: Python 3.8.10
• Django 3.2.5
• Pillow: 8.3.0 (in a venv)
• Apache (v2.4.41) / mod_wsgi (v4.6.8)

My guess

The default settings for mod_wsgi restrict access to sys.stdout.

In the interests of promoting portability of WSGI applications, mod_wsgi restricts
access to sys.stdout and will raise an exception if an attempt is made to use sys.stdout explicitly.

Recent commit 0f68e63 accesses sys.stdout explicitly in line 496 of PIL/ImageFile.py, as per the traceback above.

Thanks

Thank you for looking into this. Please let me know how I can help with testing - or anything else that might be required.