remove _valid_formatter

check in _safe_get_formatter_method

- reject classes
- allow any callable...
- ...except on objects that lazily produce callables at any attribute

IPython/core/formatters.py

@@ -39,38 +39,21 b' else:'
 #-----------------------------------------------------------------------------
 
 
-def _valid_formatter(f):
-    """Return whether an object is a valid formatter
-    
-    Cases checked:
+def _safe_get_formatter_method(obj, name):
+    """Safely get a formatter method
     
-    - bound methods             OK
-    - unbound methods           NO
-    - callable with zero args   OK
+    - Classes cannot have formatter methods, only instance
+    - protect against proxy objects that claim to have everything
     """
-    if f is None:
-        return False
-    elif isinstance(f, types.BuiltinFunctionType):
-        # bound methods on compiled classes have type builtin_function
-        return True
-    elif callable(f):
-        # anything that works with zero args should be okay
-        try:
-            inspect.getcallargs(f)
-        except Exception:
-            return False
-        else:
-            return True
-    return False
-
-def _safe_get_formatter_method(obj, name):
-    """Safely get a formatter method"""
     if inspect.isclass(obj):
         # repr methods only make sense on instances, not classes
         return None
     method = pretty._safe_getattr(obj, name, None)
-    # formatter methods must be bound
-    if _valid_formatter(method):
+    if callable(method):
+        # obj claims to have repr method...
+        if callable(pretty._safe_getattr(obj, '_ipython_canary_method_should_not_exist_', None)):
+            # ...but don't trust proxy objects that claim to have everything
+            return None
         return method
 
 

IPython/core/tests/test_formatters.py

@@ -348,8 +348,7 b' def test_print_method_weird():'
     with capture_output() as captured:
         result = f(call_hat)
     
-    nt.assert_equal(result, '_repr_html_')
-    nt.assert_not_in("FormatterWarning", captured.stderr)
+    nt.assert_equal(result, None)
 
     class BadReprArgs(object):
         def _repr_html_(self, extra, args):