Backport PR #9851: Also capture execution results using sys.displayhook

From discussion on mailing list. It's not clear if this is what we want to do, or if it should be controlled by a separate option, but it's submitted for consideration.

docs/source/whatsnew/pr/capture-displayhook.rst

@@ -0,0 +1,3 b''
+- The :cellmagic:`capture` magic can now capture the result of a cell (from an
+  expression on the last line), as well as printed and displayed output.
+  :ghpull:`9851`.

IPython/core/displayhook.py

@@ -293,3 +293,17 b' class DisplayHook(Configurable):'
         # IronPython blocks here forever
         if sys.platform != "cli":
             gc.collect()
+
+
+class CapturingDisplayHook(object):
+    def __init__(self, shell, outputs=None):
+        self.shell = shell
+        if outputs is None:
+            outputs = []
+        self.outputs = outputs
+
+    def __call__(self, result=None):
+        if result is None:
+            return
+        format_dict, md_dict = self.shell.display_formatter.format(result)
+        self.outputs.append((format_dict, md_dict))

IPython/utils/capture.py

@@ -137,6 +137,7 b' class capture_output(object):'
     def __enter__(self):
         from IPython.core.getipython import get_ipython
         from IPython.core.displaypub import CapturingDisplayPublisher
+        from IPython.core.displayhook import CapturingDisplayHook
         
         self.sys_stdout = sys.stdout
         self.sys_stderr = sys.stderr
@@ -156,7 +157,9 b' class capture_output(object):'
             self.save_display_pub = self.shell.display_pub
             self.shell.display_pub = CapturingDisplayPublisher()
             outputs = self.shell.display_pub.outputs
-            
+            self.save_display_hook = sys.displayhook
+            sys.displayhook = CapturingDisplayHook(shell=self.shell,
+                                                   outputs=outputs)
         
         return CapturedIO(stdout, stderr, outputs)
     
@@ -165,5 +168,6 b' class capture_output(object):'
         sys.stderr = self.sys_stderr
         if self.display and self.shell:
             self.shell.display_pub = self.save_display_pub
+            sys.displayhook = self.save_display_hook