drop use of imghdr

[dkg]

imghdr is deprecated and will be removed in python 3.13 (see https://peps.python.org/pep-0594/#imghdr)

The relevant code in imghdr is just:

def test_jpeg(h, f):
    """JPEG data with JFIF or Exif markers; and raw JPEG"""
    if h[6:10] in (b'JFIF', b'Exif'):
        return 'jpeg'
    elif h[:4] == b'\xff\xd8\xff\xdb':
        return 'jpeg'

So we transplant it directly

[jbkkd]

Any chance this could get merged in the near future?

[ktdreyer]

@Commod0re would you please merge this PR and ship a new release to PyPI?

I've confirmed that the implementation here matches test_jpeg() in /usr/lib64/python3.11/imghdr.py. Also, I tested this conditional on a random JPG image and imagebytes[6:10] is indeed b'JFIF'.

[etzelc]

Python 3.13 was released last week, and the imghdr module has been removed. https://www.python.org/downloads/release/python-3130/.

Are there any remaining blockers for this PR?

[sshishov]

We cannot move to Python3.13 because of this blocker.

But instead of copy-pasting the code, maybe we can try to use some alternatives proposed in PEP-0594?

These are the alternatives proposed there:

• filetype
• puremagic
• python-magic

Hope that the issue will be resolved, either by "hardcoding" the old implementation or replacing with "supported" libraries.