Fix inference of list multiplication operation.

Old implementation was pushing all the possible values inferred from a node
into a list, thus creating extra items in case when there are multiple infered
values yielded. New implementation takes only first infered value, preserving
the expected size of the list.

Fixes pylint's #559.

2 files changed, 19 insertions, 3 deletions

diff --git a/astroid/protocols.py b/astroid/protocols.py
index 23a4f2e..c51464d 100644
--- a/astroid/protocols.py
+++ b/astroid/protocols.py
@@ -141,9 +141,12 @@ nodes.Const.infer_binary_op = const_infer_binary_op
 
 def _multiply_seq_by_int(self, other, context):
     node = self.__class__()
-    elts = [n for elt in self.elts for n in elt.infer(context)
-            if not n is util.YES] * other.value
-    node.elts = elts
+    elts = []
+    for elt in self.elts:
+        infered = next(elt.infer(context))
+        if not infered is util.YES:
+            elts.append(infered)
+    node.elts = elts * other.value
     return node
 
 
diff --git a/astroid/tests/unittest_inference.py b/astroid/tests/unittest_inference.py
index bce1db4..6adaada 100644
--- a/astroid/tests/unittest_inference.py
+++ b/astroid/tests/unittest_inference.py
@@ -1018,6 +1018,19 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         self.assertEqual(len(inferred), 1)
         self.assertEqual(inferred[0], util.YES)
 
+    def test_binary_op_list_mul_int(self):
+        'test correct handling on list multiplied by int when there are more than one'
+        code = '''
+        from ctypes import c_int
+        seq = [c_int()] * 4
+        '''
+        ast = parse(code, __name__)
+        inferred = ast['seq'].inferred()
+        self.assertEqual(len(inferred), 1)
+        listval = inferred[0]
+        self.assertIsInstance(listval, nodes.List)
+        self.assertEqual(len(listval.itered()), 4)
+
     def test_binary_op_on_self(self):
         'test correct handling of applying binary operator to self'
         code = '''