Silence errors from custom attribute completer functions.

Closes ipythongh-907

IPython/core/completer.py

@@ -392,6 +392,10 @@ def attr_matches(self, text):
             words = generics.complete_object(obj, words)
         except TryNext:
             pass
+        except Exception:
+            # Silence errors from completion function
+            #raise # dbg
+            pass
         # Build match list to return
         n = len(attr)
         res = ["%s.%s" % (expr, w) for w in words if w[:n] == attr ]

IPython/core/tests/test_completer.py

@@ -16,6 +16,7 @@
 from IPython.core import completer
 from IPython.external.decorators import knownfailureif
 from IPython.utils.tempdir import TemporaryDirectory
+from IPython.utils.generics import complete_object
 
 #-----------------------------------------------------------------------------
 # Test functions
@@ -83,6 +84,18 @@ def test_line_split():
     # all inputs turned into unicode
     check_line_split(sp, [ map(unicode, p) for p in t] )
 
+def test_custom_completion_error():
+    """Test that errors from custom attribute completers are silenced."""
+    ip = get_ipython()
+    class A(object): pass
+    ip.user_ns['a'] = A()
+
+    @complete_object.when_type(A)
+    def complete_A(a, existing_completions):
+        raise TypeError("this should be silenced")
+
+    ip.complete("a.")
+
 
 def test_unicode_completions():
     ip = get_ipython()