Ignore non-callables when looking for special method implementations of bool methods

This commit verifies what a special method actually is and if it's
not a callable, then we return an YES object, since there's a big
chance to not make sense of the instance's boolean value.

2 files changed, 22 insertions, 1 deletions

diff --git a/astroid/bases.py b/astroid/bases.py
index 3656102..3ed52bf 100644
--- a/astroid/bases.py
+++ b/astroid/bases.py
@@ -126,6 +126,8 @@ def _infer_method_result_truth(instance, method_name, context):
     # its return's truth value.
     meth = next(instance.igetattr(method_name, context=context), None)
     if meth and hasattr(meth, 'infer_call_result'):
+        if not meth.callable():
+            return util.YES
         for value in meth.infer_call_result(instance, context=context):
             if value is util.YES:
                 return value
diff --git a/astroid/tests/unittest_inference.py b/astroid/tests/unittest_inference.py
index 093b076..644e282 100644
--- a/astroid/tests/unittest_inference.py
+++ b/astroid/tests/unittest_inference.py
@@ -3324,16 +3324,35 @@ class TestBool(unittest.TestCase):
         class TrueClass:
            def {method}(self):
                return True
+        class C(object):
+           def __call__(self):
+               return False
+        class B(object):
+           {method} = C()
         bool(FalseClass) #@
         bool(TrueClass) #@
         bool(FalseClass()) #@
         bool(TrueClass()) #@
+        bool(B()) #@
         '''.format(method=BOOL_SPECIAL_METHOD))
-        expected = [True, True, False, True]
+        expected = [True, True, False, True, False]
         for node, expected_value in zip(ast_nodes, expected):
             inferred = next(node.infer())
             self.assertEqual(inferred.value, expected_value)
 
+    def test_bool_instance_not_callable(self):
+        ast_nodes = test_utils.extract_node('''
+        class BoolInvalid(object):
+           {method} = 42
+        class LenInvalid(object):
+           __len__ = "a"
+        bool(BoolInvalid()) #@
+        bool(LenInvalid()) #@
+        '''.format(method=BOOL_SPECIAL_METHOD))
+        for node in ast_nodes:
+            inferred = next(node.infer())
+            self.assertEqual(inferred, util.YES)
+
 
 class TestType(unittest.TestCase):