From 9a8bdb911852f39b808bfd8cd8f1f52a6b5ae9c7 2017-11-13 14:05:43
From: Thomas Kluyver <thomas@kluyver.me.uk>
Date: 2017-11-13 14:05:43
Subject: [PATCH] Ensure that MimeBundleFormatter always returns a 2-tuple

---

diff --git a/IPython/core/formatters.py b/IPython/core/formatters.py
index e520b42..f51cce9 100644
--- a/IPython/core/formatters.py
+++ b/IPython/core/formatters.py
@@ -224,7 +224,7 @@ def catch_format_error(method, self, *args, **kwargs):
         r = method(self, *args, **kwargs)
     except NotImplementedError:
         # don't warn on NotImplementedErrors
-        return None
+        return self._check_return(None, args[0])
     except Exception:
         exc_info = sys.exc_info()
         ip = get_ipython()
@@ -232,7 +232,7 @@ def catch_format_error(method, self, *args, **kwargs):
             ip.showtraceback(exc_info)
         else:
             traceback.print_exception(*exc_info)
-        return None
+        return self._check_return(None, args[0])
     return self._check_return(r, args[0])
 
 
diff --git a/IPython/core/tests/test_formatters.py b/IPython/core/tests/test_formatters.py
index af51ffe..35edc75 100644
--- a/IPython/core/tests/test_formatters.py
+++ b/IPython/core/tests/test_formatters.py
@@ -521,3 +521,13 @@ def test_repr_mime_meta():
             'height': 10,
         }
     })
+
+def test_repr_mime_failure():
+    class BadReprMime(object):
+        def _repr_mimebundle_(self, include=None, exclude=None):
+            raise RuntimeError
+
+    f = get_ipython().display_formatter
+    obj = BadReprMime()
+    d, md = f.format(obj)
+    nt.assert_in('text/plain', d)