Merged in dmand/astroid/binop-inference-fix (pull request #92)

Fix binary operator inference issue from pylint's #646

2 files changed, 19 insertions, 7 deletions

diff --git a/astroid/inference.py b/astroid/inference.py
index 3253acb..2943596 100644
--- a/astroid/inference.py
+++ b/astroid/inference.py
@@ -582,18 +582,18 @@ def _infer_binop(self, context):
     right = self.right
     op = self.op
 
-    for lhs in left.infer(context=context):
+    # we use two separate contexts for evaluating lhs and rhs because
+    # 1. evaluating lhs may leave some undesired entries in context.path
+    #    which may not let us infer right value of rhs
+    lhs_context = context.clone()
+    rhs_context = context.clone()
+
+    for lhs in left.infer(context=lhs_context):
         if lhs is util.YES:
             # Don't know how to process this.
             yield util.YES
             return
 
-        # TODO(cpopa): if we have A() * A(), trying to infer
-        # the rhs with the same context will result in an
-        # inferrence error, so we create another context for it.
-        # This is a bug which should be fixed in InferenceContext at some point.
-        rhs_context = context.clone()
-        rhs_context.path = set()
         for rhs in right.infer(context=rhs_context):
             if rhs is util.YES:
                 # Don't know how to process this.
diff --git a/astroid/tests/unittest_inference.py b/astroid/tests/unittest_inference.py
index e3cade4..bce1db4 100644
--- a/astroid/tests/unittest_inference.py
+++ b/astroid/tests/unittest_inference.py
@@ -1018,6 +1018,18 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         self.assertEqual(len(inferred), 1)
         self.assertEqual(inferred[0], util.YES)
 
+    def test_binary_op_on_self(self):
+        'test correct handling of applying binary operator to self'
+        code = '''
+        import sys
+        sys.path = ['foo'] + sys.path
+        sys.path.insert(0, 'bar')
+        path = sys.path
+        '''
+        ast = parse(code, __name__)
+        inferred = ast['path'].inferred()
+        self.assertIsInstance(inferred[0], nodes.List)
+
     def test_binary_op_tuple_add(self):
         ast = builder.string_build('a = (1,) + (2,)', __name__, __file__)
         inferred = list(ast['a'].infer())