Edit getdata to recommend iterating in a type-correct way

[DominicOram]

Pillow/src/PIL/Image.py

Line 1436 in 5122c83

printing), use ``list(im.getdata())``.

recommends that people use list(im.getdata()) for e.g. printing data. This works fine in production but type checkers (such as pyright) do not like it as ImagingCore does not expose an __iter__. This adds that so that the type checking is happy.

Notes

• It would be better to not say that the __iter__ returns Any but I do not know the codebase well enough to know if there are variations in what types it might return. Any is sufficient to fix the type checker for my usecase

[DiamondJoseph]

Just guessing from the other methods, would it be

from collections.abc import Iterator
...

    def __getitem__(self, index: int) -> float: ...
    def __iter__(self) -> Iterator[float]: ...

Or are other elements returned also?

[radarhere]

My suggestion would be float | tuple[int, ...] | None to mirror

Pillow/src/PIL/Image.py

Lines 1631 to 1633 in 5122c83

	def getpixel(
	self, xy: tuple[int, int] | list[int]
	) -> float | tuple[int, ...] | None:

Regarding the first code you found

Pillow/src/PIL/_imaging.pyi

Line 4 in 5122c83

def __getitem__(self, index: int) -> float: ...

I think this should actually be updated as well.

def __iter__(self) -> Iterator[float]: ...

I don't know where this came from.

[tpoliaw]

>>> ic = im.getdata()
>>> ic.__iter__()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'ImagingCore' object has no attribute '__iter__'. Did you mean: '__str__'?

I think the problem is in pyright/pyshed more than pillow. The ImagingCore type has no __iter__ method so while the PR fixes the linting, it's not really accurate. Adding __len__ to the type-stub would be more correct but still wouldn't fix the problem here because the typing on the list method is too restrictive which (I think?) comes from typeshed.

A workaround that passes type-checking could be list(iter(im.getdata()))

[tpoliaw]

For completeness, I found this issue in typeshed and the upshot was that supporting __getitem__ iterators wasn't feasible and calling code should use iter.

[DominicOram]

Ok, in which case I will change the comment in

Pillow/src/PIL/Image.py

Line 1436 in 5122c83

printing), use ``list(im.getdata())``.

to suggest list(iter(im.getdata())) as it better matches the type

[radarhere]

What was your thinking behind this reformatting?

[radarhere]

What was your thinking behind this reformatting?

[radarhere]

When I test, I don't find any issue with list(im.getdata()) in mypy.

I'm a bit reluctant to tell everyone to change their code in this way - not everyone uses type checkers, and of that subset, only a third use pyright.

A simpler alternative for pyright might actually be iterating over im.tobytes().

Others may disagree with me, but if you really think there is a problem here, I'd actually be more interested in deprecating getdata() altogether.

Pillow/src/PIL/Image.py

Line 1447 in 76f04b4

return self.im # could be abused