Catch failure in repr() for %whos.

IPython/core/magic.py

@@ -953,6 +953,8 b' Currently the magic system has the following functions:\\n"""'
                 except UnicodeEncodeError:
                     vstr = unicode(var).encode(DEFAULT_ENCODING,
                                                'backslashreplace')
+                except:
+                    vstr = "<object with id %d (repr failed)>" % id(var)
                 vstr = vstr.replace('\n','\\n')
                 if len(vstr) < 50:
                     print vstr

IPython/core/tests/test_magic.py

@@ -376,6 +376,14 b' def doctest_who():'
     Out[7]: ['alpha', 'beta']
     """
 
+def test_whos():
+    """Check that whos is protected against objects where repr() fails."""
+    class A(object):
+        def __repr__(self):
+            raise Exception()
+    _ip.user_ns['a'] = A()
+    _ip.magic("whos")
+
 @py3compat.u_format
 def doctest_precision():
     """doctest for %precision