bpo-38870: Throw ValueError on invalid yield from usage (GH-17798)
diff --git a/Lib/ast.py b/Lib/ast.py
index 62f6e07..ece8b13 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -735,10 +735,10 @@
def visit_YieldFrom(self, node):
with self.delimit("(", ")"):
- self.write("yield from")
- if node.value:
- self.write(" ")
- self.traverse(node.value)
+ self.write("yield from ")
+ if not node.value:
+ raise ValueError("Node can't be used without a value attribute.")
+ self.traverse(node.value)
def visit_Raise(self, node):
self.fill("raise")
diff --git a/Lib/test/test_unparse.py b/Lib/test/test_unparse.py
index 49767db..e8b0d4b 100644
--- a/Lib/test/test_unparse.py
+++ b/Lib/test/test_unparse.py
@@ -278,6 +278,8 @@
def test_invalid_set(self):
self.check_invalid(ast.Set(elts=[]))
+ def test_invalid_yield_from(self):
+ self.check_invalid(ast.YieldFrom(value=None))
class DirectoryTestCase(ASTTestCase):
"""Test roundtrip behaviour on all files in Lib and Lib/test."""