bpo-35877: Make parenthesis optional for named expression in while statement (GH-11724)

* Add parenthesis optional in named expressions for while statement

* Add NEWS entry

Grammar/Grammar

@@ -72,7 +72,7 @@ assert_stmt: 'assert' test [',' test]
 compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt | with_stmt | funcdef | classdef | decorated | async_stmt
 async_stmt: 'async' (funcdef | with_stmt | for_stmt)
 if_stmt: 'if' namedexpr_test ':' suite ('elif' namedexpr_test ':' suite)* ['else' ':' suite]
-while_stmt: 'while' test ':' suite ['else' ':' suite]
+while_stmt: 'while' namedexpr_test ':' suite ['else' ':' suite]
 for_stmt: 'for' exprlist 'in' testlist ':' [TYPE_COMMENT] suite ['else' ':' suite]
 try_stmt: ('try' ':' suite
            ((except_clause ':' suite)+

Lib/test/test_parser.py

@@ -426,6 +426,7 @@ def test_named_expressions(self):
         self.check_suite("(a := 1)")
         self.check_suite("(a := a)")
         self.check_suite("if (match := pattern.search(data)) is None: pass")
+        self.check_suite("while match := pattern.search(f.read()): pass")
         self.check_suite("[y := f(x), y**2, y**3]")
         self.check_suite("filtered_data = [y for x in data if (y := f(x)) is None]")
         self.check_suite("(y := f(x))")

Misc/NEWS.d/next/Core and Builtins/2019-02-01-22-38-11.bpo-35877.Jrse8f.rst

@@ -0,0 +1,2 @@
+Make parenthesis optional for named expressions in while statement. Patch by
+Karthikeyan Singaravelan.

Python/graminit.c

@@ -971,7 +971,7 @@ static arc arcs_42_0[1] = {
     {103, 1},
 };
 static arc arcs_42_1[1] = {
-    {26, 2},
+    {99, 2},
 };
 static arc arcs_42_2[1] = {
     {27, 3},