Added IPythonViewer

Tests/test_imageshow.py

@@ -62,4 +62,20 @@ def test_viewer():
 
 def test_viewers():
     for viewer in ImageShow._viewers:
-        viewer.get_command("test.jpg")
+        try:
+            viewer.get_command("test.jpg")
+        except NotImplementedError:
+            pass
+
+
+def test_ipythonviewer():
+    pytest.importorskip("IPython", reason="IPython not installed")
+    for viewer in ImageShow._viewers:
+        if isinstance(viewer, ImageShow.IPythonViewer):
+            test_viewer = viewer
+            break
+    else:
+        assert False
+
+    im = hopper()
+    assert test_viewer.show(im) == 1

docs/reference/ImageShow.rst

@@ -9,6 +9,7 @@ All default viewers convert the image to be shown to PNG format.
 
 .. autofunction:: PIL.ImageShow.show
 
+.. autoclass:: IPythonViewer
 .. autoclass:: WindowsViewer
 .. autoclass:: MacViewer
 

docs/releasenotes/8.2.0.rst

@@ -21,10 +21,17 @@ TODO
 API Additions
 =============
 
-TODO
-^^^^
+ImageShow.IPythonViewer
+^^^^^^^^^^^^^^^^^^^^^^^
 
-TODO
+If IPython is present, this new ``ImageShow.Viewer`` subclass will be
+registered. It displays images on all IPython frontends. This will be helpful
+to users of Google Colab, allowing ``im.show()`` to display images.
+
+It is lower in priority than the other default Viewer instances, so it will
+only be used by ``im.show()`` or ``ImageShow.show()`` if none of the other
+viewers are available. This means that the behaviour of ``ImageShow`` will stay
+the same for most Pillow users.
 
 Security
 ========

src/PIL/ImageShow.py

@@ -225,6 +225,23 @@ def get_command_ex(self, file, title=None, **options):
     if shutil.which("xv"):
         register(XVViewer)
 
+
+class IPythonViewer(Viewer):
+    """The viewer for IPython frontends."""
+
+    def show_image(self, image, **options):
+        ipython_display(image)
+        return 1
+
+
+try:
+    from IPython.display import display as ipython_display
+except ImportError:
+    pass
+else:
+    register(IPythonViewer)
+
+
 if __name__ == "__main__":
 
     if len(sys.argv) < 2: