bpo-38870: Don't omit parenthesis when unparsing a slice in ast.unparse
When unparsing a non-empty tuple, the parentheses can be safely
omitted if there aren't any elements that explicitly require them (such as starred expressions).
diff --git a/Lib/ast.py b/Lib/ast.py
index 2edb717..52e51b4 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -1356,10 +1356,20 @@
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
index 6d82872..bb725ce 100644
--- a/Lib/test/test_unparse.py
+++ b/Lib/test/test_unparse.py
@@ -279,10 +279,13 @@
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]")
@@ -470,6 +473,11 @@
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."""