* moved all namedexpr_test related rules to _NamedExprRule

 * added valid examples

parso/python/errors.py

@@ -125,19 +125,6 @@ def _get_for_stmt_definition_exprs(for_stmt):
     return list(_iter_definition_exprs_from_lists(exprlist))
 
 
-def _get_namedexpr(node):
-    """Get assignment expression if node contains."""
-    namedexpr_list = list()
-
-    def fetch_namedexpr(node):
-        if node.type == 'namedexpr_test':
-            namedexpr_list.append(node)
-        if hasattr(node, 'children'):
-            [fetch_namedexpr(child) for child in node.children]
-
-    fetch_namedexpr(node)
-    return namedexpr_list
-
 
 class _Context(object):
     def __init__(self, node, add_syntax_error, parent_context=None):
@@ -979,14 +966,6 @@ def is_issue(self, node):
         if expr_list.type != 'expr_list':  # Already handled.
             self._check_assignment(expr_list)
 
-        or_test = node.children[3]
-        expr_list = _get_namedexpr(or_test)
-        for expr in expr_list:
-            # [i+1 for i in (i := range(5))]
-            # [i+1 for i in (j := range(5))]
-            # [i+1 for i in (lambda: (j := range(5)))()]
-            self.add_issue(expr, message='assignment expression cannot be used in a comprehension iterable expression')
-
         return node.parent.children[0] == 'async' \
             and not self._normalizer.context.is_async_funcdef()
 
@@ -1040,8 +1019,24 @@ class _NamedExprRule(_CheckAssignmentRule):
     # namedexpr_test: test [':=' test]
 
     def is_issue(self, namedexpr_test):
+        # assigned name
         first = namedexpr_test.children[0]
 
+        def search_namedexpr_in_comp_for(node):
+            while True:
+                parent = node.parent
+                if parent is None:
+                    return parent
+                if parent.type == 'sync_comp_for' and parent.children[3] == node:
+                    return parent
+                node = parent
+
+        if search_namedexpr_in_comp_for(namedexpr_test):
+            # [i+1 for i in (i := range(5))]
+            # [i+1 for i in (j := range(5))]
+            # [i+1 for i in (lambda: (j := range(5)))()]
+            self.add_issue(namedexpr_test, message='assignment expression cannot be used in a comprehension iterable expression')
+
         # defined names
         exprlist = list()
 

test/test_python_errors.py

@@ -293,6 +293,19 @@ def test_valid_fstrings(code):
     assert not _get_error_list(code, version='3.6')
 
 
+@pytest.mark.parametrize(
+    'code', [
+        'a = (b := 1)',
+        '[x4 := x ** 5 for x in range(7)]',
+        '[total := total + v for v in range(10)]',
+        'while chunk := file.read(2):\n pass',
+        'numbers = [y := math.factorial(x), y**2, y**3]',
+    ]
+)
+def test_valid_namedexpr(code):
+    assert not _get_error_list(code, version='3.8')
+
+
 @pytest.mark.parametrize(
     ('code', 'message'), [
         ("f'{1+}'", ('invalid syntax')),