"UnboundLocalError: local variable 'values' referenced before assignment" when image.getexif().tobytes() on specific JPEGs

[christophebiocca]

I can't post the picture itself because it's from a customer, but the offending exif data trying to be serialized is:

ifd: <PIL.TiffImagePlugin.ImageFileDirectory_v2 object at ...>
ifd.self._tags_v2.items : {34665: {}, 40962: 1920, 40963: 1440, 40961: 1}

That empty dictionary for 34665 seems to be the culprit.

The failing statement is the use of str(values) when is_ifd is true (and thus values never gets defined):

Pillow/src/PIL/TiffImagePlugin.py

Line 840 in 70ef50c

"<table: %d bytes>" % len(data) if len(data) >= 16 else str(values)

This will silently do the wrong thing instead of exploding if this is the second+ tag being serialized (as it will inherit values from the previous iteration of the loop.
It probably won't take that path for non-empty dictionaries, as those would have non-trivial data length.

A simple fix would be if len(data) >= 16 or is_ifd but I'm not super familiar with the codebase so it may not be the best choice.

[radarhere]

Thanks for your analysis of the problem.

I've created #5556 to resolve this, with a simple test case. Rather than using or is_ifd, my suggestion is instead to set values when is_ifd is true as well.