Added IPythonViewer

[radarhere]

Resolves #5286 by adding a new ImageShow.Viewer - IPythonViewer. It calls the display() method to allow ImageShow to work with IPython... and Google Colab.

Here is my demonstration of it working in Google Colab.

from PIL import Image, ImageShow
im = Image.new("RGB", (100, 100))
im.show()

from PIL import ImageShow
class IPythonViewer(ImageShow.Viewer):
    def show_image(self, image, **options):
        display(image)
        return 1

try:
    from IPython.display import display
except ImportError:
    pass
else:
    ImageShow.register(IPythonViewer)

from PIL import Image
im = Image.new("RGB", (100, 100))
im.show()

# Cleanup
ImageShow._viewers = [v for v in ImageShow._viewers if v.__class__ != IPythonViewer]

[nulano]

This should be very useful! Even if it takes a while until the changes reach Colab, it is not difficult to upgrade Pillow manually anyway.

[nulano]

Suggested change

	from IPython.display import display
	from IPython.display import display as _display

Would it be reasonable to add a prefix to avoid confusion when using code completion tools? ImageShow.show and ImageShow.display are very similar and could be confusing to someone using it for the first time.

[radarhere]

Okay, sure. I went with ipython_display, to be even clearer.

[nulano]

Any reason to put IPythonViewer before the unix viewers but after the other Windows/macOS ones? I think it would be best to put this at the top (or use register(..., order=0)) to help consistency in IPython (e.g. when combined with tools that offer PDF exports, etc.).

[radarhere]

Yep, no reason. I've moved it up.

[nulano]

Suggested change

	pass
	assert viewer.show(hopper()) == 1

Would remove the need for a separate test.

[radarhere]

The separate test

• confirms that the IPythonViewer is present when IPython is available
• runs IPythonViewer even if another Viewer instance has priority

Also, IPython seems to be a special case, where running its Viewer doesn't disrupt the test process - thinking generically for the sake of the future, just because a Viewer isn't based on a command line instruction doesn't mean that we want it to run in the middle of the test suite?

[nulano]

It is lower in priority than the other default Viewer instances

Please correct me if I'm wrong, but this is false. The new viewer has the highest priority AFAICT

[radarhere]

You're right! Thanks for catching that. However, the documentation correctly states my intention, so I've updated the code to match it.