From 45753395f18376a92ce7651be9f9af44126315d6 Mon Sep 17 00:00:00 2001
From: Claudiu Popa <pcmanticore@gmail.com>
Date: Sun, 2 Jun 2019 11:20:21 +0200
Subject: [PATCH] ``assert`` only functions are properly inferred as returning
 ``None``

Close #668
---
 ChangeLog                           |  4 ++++
 astroid/scoped_nodes.py             |  8 +++++++-
 astroid/tests/unittest_inference.py | 14 ++++++++++++++
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 64a300d002..921c86c615 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -25,6 +25,10 @@ Release Date: TBA
   Close PyCQA/pylint#2326
   Close PyCQA/pylint#2021
 
+* ``assert`` only functions are properly inferred as returning ``None``
+
+  Close #668
+
 * Add support for Python 3.8's `NamedExpr` nodes, which is part of assignment expressions.
 
   Close #674
diff --git a/astroid/scoped_nodes.py b/astroid/scoped_nodes.py
index bd0b7bd419..ccea388565 100644
--- a/astroid/scoped_nodes.py
+++ b/astroid/scoped_nodes.py
@@ -1656,7 +1656,13 @@ def infer_call_result(self, caller=None, context=None):
 
         first_return = next(returns, None)
         if not first_return:
-            raise exceptions.InferenceError("Empty return iterator")
+            if self.body and isinstance(self.body[-1], node_classes.Assert):
+                yield node_classes.Const(None)
+                return
+
+            raise exceptions.InferenceError(
+                "The function does not have any return statements"
+            )
 
         for returnnode in itertools.chain((first_return,), returns):
             if returnnode.value is None:
diff --git a/astroid/tests/unittest_inference.py b/astroid/tests/unittest_inference.py
index 1f9c7e447f..59cc23a6be 100644
--- a/astroid/tests/unittest_inference.py
+++ b/astroid/tests/unittest_inference.py
@@ -5289,5 +5289,19 @@ def both_branches():
     assert [third[0].value, third[1].value] == [1, 2]
 
 
+def test_assert_last_function_returns_none_on_inference():
+    code = """
+    def check_equal(a, b):
+        res = do_something_with_these(a, b)
+        assert a == b == res
+
+    check_equal(a, b)
+    """
+    node = extract_node(code)
+    inferred = next(node.infer())
+    assert isinstance(inferred, nodes.Const)
+    assert inferred.value is None
+
+
 if __name__ == "__main__":
     unittest.main()