python · pablogsal · May 18, 2020 · May 17, 2020 · May 18, 2020 · May 18, 2020
diff --git a/Lib/ast.py b/Lib/ast.py
@@ -1346,10 +1346,20 @@ def visit_Call(self, node):
                self.traverse(e)

    def visit_Subscript(self, node):
+        def is_simple_tuple(slice_value):
+            # when unparsing a non-empty tuple, the parantheses can be safely
+            # omitted if there aren't any elements that explicitly requires
+            # parantheses (such as starred expressions).
+            return (
+                isinstance(slice_value, Tuple)
+                and slice_value.elts
+                and not any(isinstance(elt, Starred) for elt in slice_value.elts)
+            )
+
        self.set_precedence(_Precedence.ATOM, node.value)
        self.traverse(node.value)
        with self.delimit("[", "]"):
-            if isinstance(node.slice, Tuple) and node.slice.elts:
+            if is_simple_tuple(node.slice):
                self.items_view(self.traverse, node.slice.elts)
            else:
                self.traverse(node.slice)

diff --git a/Lib/test/test_unparse.py b/Lib/test/test_unparse.py
@@ -279,10 +279,13 @@ def test_dict_unpacking_in_dict(self):
        self.check_ast_roundtrip(r"""{**{'y': 2}, 'x': 1}""")
        self.check_ast_roundtrip(r"""{**{'y': 2}, **{'x': 1}}""")

-    def test_ext_slices(self):
+    def test_slices(self):
        self.check_ast_roundtrip("a[i]")
        self.check_ast_roundtrip("a[i,]")
        self.check_ast_roundtrip("a[i, j]")
+        self.check_ast_roundtrip("a[(*a,)]")
+        self.check_ast_roundtrip("a[(a:=b)]")
+        self.check_ast_roundtrip("a[(a:=b,c)]")
        self.check_ast_roundtrip("a[()]")
        self.check_ast_roundtrip("a[i:j]")
        self.check_ast_roundtrip("a[:j]")
@@ -466,6 +469,11 @@ def test_unary_op_factor(self):
        for prefix in ("not",):
            self.check_src_roundtrip(f"{prefix} 1")

+    def test_slices(self):
+        self.check_src_roundtrip("a[1]")
+        self.check_src_roundtrip("a[1, 2]")
+        self.check_src_roundtrip("a[(1, *a)]")
+
 class DirectoryTestCase(ASTTestCase):
    """Test roundtrip behaviour on all files in Lib and Lib/test."""