Infer the unary method retrieved from classes.

2 files changed, 16 insertions, 2 deletions

diff --git a/astroid/inference.py b/astroid/inference.py
index fda5f2e..05428de 100644
--- a/astroid/inference.py
+++ b/astroid/inference.py
@@ -397,8 +397,9 @@ def _infer_unaryop(self, context=None):
 
                 try:
                     meth = operand.getattr(meth, context=context)[0]
-                    result = next(meth.infer_call_result(self, context=context),
-                                  None)
+                    inferred = next(meth.infer(context=context))
+                    call_results = inferred.infer_call_result(self, context=context)
+                    result = next(call_results, None)
                     if result is None:
                         # Failed to infer, return the same type.
                         yield operand
diff --git a/astroid/tests/unittest_inference.py b/astroid/tests/unittest_inference.py
index 87e6993..eba665c 100644
--- a/astroid/tests/unittest_inference.py
+++ b/astroid/tests/unittest_inference.py
@@ -2658,6 +2658,19 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         self.assertIsInstance(inferred, nodes.Const)
         self.assertEqual(inferred.value, "lala")
 
+    def test_unary_op_assignment(self):
+        ast_node = test_utils.extract_node('''
+        class A(object): pass
+        def pos(self):
+            return 42
+        A.__pos__ = pos
+        f = A()
+        +f #@
+        ''')
+        inferred = next(ast_node.infer())
+        self.assertIsInstance(inferred, nodes.Const)
+        self.assertEqual(inferred.value, 42)
+
 
 class GetattrTest(unittest.TestCase):