avoid setting explicit "None" as StopIteration exception value in generators...

avoid setting explicit "None" as StopIteration exception value in generators and directly return NULL instead

Cython/Compiler/Nodes.py

@@ -5501,10 +5501,10 @@ class ReturnStatNode(StatNode):
                         have_gil=self.in_nogil_context)
             elif self.in_generator:
                 # return value == raise StopIteration(value), but uncatchable
-                code.putln(
-                    "%s = NULL; PyErr_SetObject(PyExc_StopIteration, %s);" % (
-                        Naming.retval_cname,
-                        self.value.result_as(self.return_type)))
+                code.putln("%s = NULL;" % Naming.retval_cname)
+                if not self.value.is_none:
+                    code.putln("PyErr_SetObject(PyExc_StopIteration, %s);" %
+                        self.value.result_as(self.return_type))
                 self.value.generate_disposal_code(code)
             else:
                 self.value.make_owned_reference(code)
@@ -5516,6 +5516,9 @@ class ReturnStatNode(StatNode):
             self.value.free_temps(code)
         else:
             if self.return_type.is_pyobject:
+                if self.in_generator:
+                    code.putln("%s = NULL;" % Naming.retval_cname)
+                else:
                     code.put_init_to_py_none(Naming.retval_cname, self.return_type)
             elif self.return_type.is_returncode:
                 self.put_return(code, self.return_type.default_value)

tests/run/generators.pyx

@@ -293,6 +293,7 @@ def test_decorated(*args):
     for i in args:
         yield i
 
+
 def test_return(a):
     """
     >>> d = dict()
@@ -309,6 +310,59 @@ def test_return(a):
     a['i_was_here'] = True
     return
 
+
+def test_return_in_finally(a):
+    """
+    >>> d = dict()
+    >>> obj = test_return_in_finally(d)
+    >>> next(obj)
+    1
+    >>> next(obj)
+    Traceback (most recent call last):
+    StopIteration
+    >>> d['i_was_here']
+    True
+
+    >>> obj = test_return_in_finally(None)
+    >>> next(obj)
+    1
+    >>> next(obj)
+    Traceback (most recent call last):
+    StopIteration
+    """
+    yield 1
+    try:
+        a['i_was_here'] = True
+    finally:
+        return
+
+
+def test_return_none_in_finally(a):
+    """
+    >>> d = dict()
+    >>> obj = test_return_none_in_finally(d)
+    >>> next(obj)
+    1
+    >>> next(obj)
+    Traceback (most recent call last):
+    StopIteration
+    >>> d['i_was_here']
+    True
+
+    >>> obj = test_return_none_in_finally(None)
+    >>> next(obj)
+    1
+    >>> next(obj)
+    Traceback (most recent call last):
+    StopIteration
+    """
+    yield 1
+    try:
+        a['i_was_here'] = True
+    finally:
+        return None
+
+
 def test_copied_yield(foo):
     """
     >>> class Manager(object):