Use _repr_mimebundle_ in IPython 6.1 or later.

Fixes jupyter-widgets#1811

ipywidgets/widgets/tests/test_widget.py

@@ -3,10 +3,10 @@
 
 """Test Widget."""
 
+from IPython import version_info
 from IPython.core.interactiveshell import InteractiveShell
 from IPython.display import display
 from IPython.utils.capture import capture_output
-
 from ..widget import Widget
 
 
@@ -19,6 +19,10 @@ def test_no_widget_view():
         w = Widget()
         display(w)
 
-    assert cap.outputs == [], repr(cap.outputs)
+    if version_info >= (6, 1):
+        assert len(cap.outputs) == 1 and cap.outputs[0].data['text/plain'] == 'Widget()', repr(cap.outputs)
+    else:
+        assert cap.outputs == [], repr(cap.outputs)
+
     assert cap.stdout == '', repr(cap.stdout)
     assert cap.stderr == '', repr(cap.stderr)

ipywidgets/widgets/widget.py

@@ -9,6 +9,7 @@
 import collections
 import sys
 
+from IPython import version_info as ipython_version_info
 from IPython.core.getipython import get_ipython
 from ipykernel.comm import Comm
 from traitlets.utils.importstring import import_item
@@ -466,6 +467,7 @@ def close(self):
             self.comm.close()
             self.comm = None
             self._ipython_display_ = None
+            self._repr_mimebundle_ = None
 
     def send_state(self, key=None):
         """Sends the widget state, or a piece of it, to the front-end, if it exists.
@@ -697,9 +699,12 @@ def _trait_from_json(x, self):
         """Convert json values to objects."""
         return x
 
-    def _ipython_display_(self, **kwargs):
-        """Called when `IPython.display.display` is called on the widget."""
+    def _repr_mimebundle_(self, **kwargs):
+        """Called when `IPython.display.display` is called."""
         if self._view_name is not None:
+            # This callback now happens *before* the actual display call,
+            # whereas before it happened *after* the display call.
+            self._handle_displayed(**kwargs)
 
             plaintext = repr(self)
             if len(plaintext) > 110:
@@ -717,9 +722,20 @@ def _ipython_display_(self, **kwargs):
                     'model_id': self._model_id
                 }
             }
-            display(data, raw=True)
+            return data
 
-            self._handle_displayed(**kwargs)
+    def _ipython_display_(self, **kwargs):
+        """Called when `IPython.display.display` is called on a widget.
+
+        Note: if we are in IPython 6.1 or later, we return NotImplemented so
+        that _repr_mimebundle_ is used directly.
+        """
+        if ipython_version_info >= (6, 1):
+            raise NotImplementedError
+
+        data = self._repr_mimebundle_(**kwargs)
+        if data:
+            display(data, raw=True)
 
     def _send(self, msg, buffers=None):
         """Sends a message to the model in the front-end."""