[3.8] bpo-40355: Improve error messages in ast.literal_eval with malformed Dict nodes (GH-19868)

Lib/ast.py

@@ -59,11 +59,12 @@ def literal_eval(node_or_string):
  node_or_string = parse(node_or_string, mode='eval')
  if isinstance(node_or_string, Expression):
  node_or_string = node_or_string.body
+ def _raise_malformed_node(node):
+ raise ValueError(f'malformed node or string: {node!r}')
  def _convert_num(node):
- if isinstance(node, Constant):
- if type(node.value) in (int, float, complex):
- return node.value
- raise ValueError('malformed node or string: ' + repr(node))
+ if not isinstance(node, Constant) or type(node.value) not in (int, float, complex):
+ _raise_malformed_node(node)
+ return node.value
  def _convert_signed_num(node):
  if isinstance(node, UnaryOp) and isinstance(node.op, (UAdd, USub)):
  operand = _convert_num(node.operand)
@@ -82,6 +83,8 @@ def _convert(node):
  elif isinstance(node, Set):
  return set(map(_convert, node.elts))
  elif isinstance(node, Dict):
+ if len(node.keys) != len(node.values):
+ _raise_malformed_node(node)
  return dict(zip(map(_convert, node.keys),
  map(_convert, node.values)))
  elif isinstance(node, BinOp) and isinstance(node.op, (Add, Sub)):

Lib/test/test_ast.py

@@ -869,6 +869,12 @@ def test_literal_eval_complex(self):
  self.assertRaises(ValueError, ast.literal_eval, '3+(0+6j)')
  self.assertRaises(ValueError, ast.literal_eval, '-(3+6j)')
 
+ def test_literal_eval_malformed_dict_nodes(self):
+ malformed = ast.Dict(keys=[ast.Constant(1), ast.Constant(2)], values=[ast.Constant(3)])
+ self.assertRaises(ValueError, ast.literal_eval, malformed)
+ malformed = ast.Dict(keys=[ast.Constant(1)], values=[ast.Constant(2), ast.Constant(3)])
+ self.assertRaises(ValueError, ast.literal_eval, malformed)
+
  def test_bad_integer(self):
  # issue13436: Bad error message with invalid numeric values
  body = [ast.ImportFrom(module='time',

Misc/NEWS.d/next/Library/2020-05-02-14-24-48.bpo-40355.xTujaB.rst

@@ -0,0 +1,2 @@
+Improve error reporting in :func:`ast.literal_eval` in the presence of malformed :class:`ast.Dict`
+nodes instead of silently ignoring any non-conforming elements. Patch by Curtis Bucher.