Merge pull request #1495 from rkern/fix-hyperobject-pprint

BUG: Fix pretty-printing for overzealous objects

Some classes use __getattr__ to automatically create requested attributes. The recent trend of LINQ-like query objects is what I ran into. This confuses the pretty-printing machinery that tests for _repr_pretty_. This pull request fixes many of these problems by simply testing if the _repr_pretty_ attribute is callable. This may still be confused by certain mocking frameworks, but it's a good start.

IPython/core/tests/test_formatters.py

@@ -10,6 +10,7 b' except:'
 import nose.tools as nt
 
 from IPython.core.formatters import FormatterABC, PlainTextFormatter
+from IPython.lib import pretty
 
 class A(object):
     def __repr__(self):
@@ -19,6 +20,16 b' class B(A):'
     def __repr__(self):
         return 'B()'
 
+class BadPretty(object):
+    _repr_pretty_ = None
+
+class GoodPretty(object):
+    def _repr_pretty_(self, pp, cycle):
+        pp.text('foo')
+
+    def __repr__(self):
+        return 'GoodPretty()'
+
 def foo_printer(obj, pp, cycle):
     pp.text('foo')
 
@@ -27,9 +38,15 b' def test_pretty():'
     f.for_type(A, foo_printer)
     nt.assert_equals(f(A()), 'foo')
     nt.assert_equals(f(B()), 'foo')
+    nt.assert_equals(f(GoodPretty()), 'foo')
+    # Just don't raise an exception for the following:
+    f(BadPretty())
+
     f.pprint = False
     nt.assert_equals(f(A()), 'A()')
     nt.assert_equals(f(B()), 'B()')
+    nt.assert_equals(f(GoodPretty()), 'GoodPretty()')
+
 
 def test_deferred():
     f = PlainTextFormatter()

IPython/lib/pretty.py

@@ -347,6 +347,10 b' class RepresentationPrinter(PrettyPrinter):'
                         return printer(obj, self, cycle)
             # Finally look for special method names.
             if hasattr(obj_class, '_repr_pretty_'):
+                # Some objects automatically create any requested
+                # attribute. Try to ignore most of them by checking for
+                # callability.
+                if callable(obj_class._repr_pretty_):
                 return obj_class._repr_pretty_(obj, self, cycle)
             return _default_pprint(obj, self, cycle)
         finally: