Fix tkinter ImageSpec #11721

[kbaikov]

Fixes #11721

[kbaikov]

@srittau Do i need to comment Any here too? If so what would be the appropriate comment.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[Akuli]

Thanks for working on this! Tkinter is more tricky than you'd expect :)

After thinking about this again, I'm pretty sure that using Any is not a good idea. The problem is that it doesn't detect the following mistake, which is easy to make and gives a misleading error message at runtime:

import tkinter
import PIL.Image

root = tkinter.Tk()
img = PIL.Image.open("foo.png")
label = tkinter.Label(image=img)

The problem is that you forgot to wrap the PIL image in a PIL.ImageTk image. This is the correct code:

import tkinter
import PIL.Image
import PIL.ImageTk

root = tkinter.Tk()
img = PIL.Image.open("foo.png")
img_tk = PIL.ImageTk.PhotoImage(img)
label = tkinter.Label(root, image=img_tk)

To make type checkers complain about the wrong code, let's use the following protocol:

class _ImageLike(Protocol):
    def width(self) -> int: ...
    def height(self) -> int: ...

This matches tkinter's image classes (PhotoImage and BitmapImage) and PIL's tkinter-compatible class (PIL.ImageTk.PhotoImage), but not a plain PIL image that isn't tkinter compatible. The reason is that PIL has width and height attributes, not methods:

>>> img.width
788
>>> img_tk.width
<bound method PhotoImage.width of <PIL.ImageTk.PhotoImage object at 0x7fb2712e6510>>

Do you want to change this PR, or do you want me to make a new PR with the protocol?

[Akuli]

Apparently this has been a protocol before, but it was changed in #9733. There I said:

I'll probably merge this in a few days, unless someone comes up with a better idea or some reasoning to prefer the width(),height() protocol over fake classes.

And now that PIL ships its own type stubs, that is a good reason to prefer a protocol over fake classes that don't really work anymore.