[BUG] Changing the files even if the exif is empty

[Lee-W]

Required attestation

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of exif-stripper.
• I have confirmed this bug exists on the main branch of exif-stripper.

Describe the bug
Exif-stripper cleans and saves image files even when there is no EXIF data to remove, which causes the pre-commit hook to fail.

To Reproduce

# Change the directory to some place for testing
cd /tmp
mkdir test-exif-stripper
cd test-exif-stripper

# set up git for the project
git init

# [manual step] move some images to test-exif-stripper directory

git add .
pre-commit install
git cmt -m "add new images"

The pre-commit keeps showing

strip-exif....................................................................Failed
- hook id: strip-exif
- exit code: 1

Stripped metadata from ...

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
If applicable, add screenshots to help explain your problem.

Environment

• OS: [e.g. iOS] macOS 15.1
• Browser [e.g. chrome, safari] -
• Python Version [e.g. 22] 3.13.0
• pillow version: 11.0.0
• xattr version, if not using Windows: 1.1.0

Additional context

This is due to

exif-stripper/src/exif_stripper/__init__.py

Line 31 in d387c8b

if exif := im.getexif():

. It does not return None even if there's no data.

[github-actions]

It looks like this is your first issue here – welcome! Please familiarize yourself with the contributing guidelines, if you haven't already.

[stefmolin]

Hi @Lee-W, nice to hear from you 😊

Your example mentions moving some images, but you don't provide any examples for me to test. I have also not seen this happen on my machine, so I really need a reproducible example here.

If you see the pre-commit failure after adding the images, remember that you need to do git add . after the hook changes them as well. Otherwise, pre-commit stashes the changes that exif-stripper made (which are unstaged) and then it will continue to fail (because it is still running on the original file).

---

I'm also not seeing an issue with the line you reference. You can confirm this by running the following test, which succeeds because the EXIF is falsey:

def test_empty_exif(tmp_path):
    image_file = tmp_path / 'test.png'
    with Image.new(mode='1', size=(2, 2)) as im:
        im.save(image_file)
    assert not im.getexif()

While the EXIF class does not have a __bool__() method, Python also checks __len__() (see "Truth Value Testing" in the Python docs):

By default, an object is considered true unless its class defines either a __bool__() method that returns False or a __len__() method that returns zero, when called with the object.

[Lee-W]

Hi @Lee-W, nice to hear from you 😊

Thank you for your kind words about commitizen on the podcast! 🙌

Your example mentions moving some images, but you don't provide any examples for me to test. I have also not seen this happen on my machine, so I really need a reproducible example here.

Any image would failed on my machine 🤔 (a bit more detail below)

If you see the pre-commit failure after adding the images, remember that you need to do git add . after the hook changes them as well. Otherwise, pre-commit stashes the changes that exif-stripper made (which are unstaged) and then it will continue to fail (because it is still running on the original file).

I'm also not seeing an issue with the line you reference. You can confirm this by running the following test, which succeeds because the EXIF is falsey:

def test_empty_exif(tmp_path):
    image_file = tmp_path / 'test.png'
    with Image.new(mode='1', size=(2, 2)) as im:
        im.save(image_file)
    assert not im.getexif()

While the EXIF class does not have a __bool__() method, Python also checks __len__() (see "Truth Value Testing" in the Python docs):

By default, an object is considered true unless its class defines either a __bool__() method that returns False or a __len__() method that returns zero, when called with the object.

Ah, you're right 🤦‍♂️ By the time I saw the object was returned, I thought this was the root cause, which turns out it is not 🤦‍♂️ I tested it a bit more and found out it's actually due to

exif-stripper/src/exif_stripper/__init__.py

Lines 43 to 44 in d387c8b

	if xattr_obj.list():
	xattr_obj.clear()

. It's likely a mac specific thing. Did a quick survey https://apple.stackexchange.com/questions/450118/what-is-the-com-apple-provenance-xattr-extended-attribute-and-how-can-i-dele. It's even possibly a terminal-specific thing 🤔 (I'm using iTerm), but even I change it to terminal.app it still fails. Will did into it a bit more and see what's happening

[Lee-W]

I just verified on my machine this com.apple.provenance xattr is something that cannot be removed by xattr lib on macOS. I also tried the commands mentioned in the article. Still cannot remove it

[stefmolin]

Hmm, I have the same setup as you (macOS and iTerm). From what I gathered, it is related to the permissions you give to iTerm (see #4 (comment)). Another user mentioned having an issue with a different attribute that I also wasn't able to replicate, so I want to do more research on extended attributes before proceeding.

[Lee-W]

Hmm, I have the same setup as you (macOS and iTerm). From what I gathered, it is related to the permissions you give to iTerm (see #4 (comment)). Another user mentioned having an issue with a different attribute that I also wasn't able to replicate, so I want to do more research on extended attributes before proceeding.

I tried to research a bit, but it seems to be an internal thing without an explicit document. (or simply I just did not find it 🥲) But instead of skipping some tags like what I do now in #57. I'm thinking of another solution.

The has_changed value here and here does not actually reflect whether the value has been changed (in most case yes), but whether the value has been cleaned. If there's any value that cannot be cleaned due to some reason, the has_changed value would still be true while it probably should not be. I'm thinking of comparing the list before and after cleaning the attributed and set this value. If the value is False, but the attribute is still not empty, we can raise a warning. WDYT?

[stefmolin]

That sounds like a better idea, but let's only do it for the extended attributes (xattr). The current behavior will result in being unable to commit images in which we can't remove the EXIF metadata, and that is a behavior I want to preserve.

[Lee-W]

That sounds like a better idea, but let's only do it for the extended attributes (xattr). The current behavior will result in being unable to commit images in which we can't remove the EXIF metadata, and that is a behavior I want to preserve.

sounds good! just removed the exif part and do it on xattr only