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gh-77069: add context info to ast.literal_eval error messages by isidentical · Pull Request #17662 · python/cpython · GitHub

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gh-77069: add context info to ast.literal_eval error messages #17662

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gh-77069: add context info to ast.literal_eval error messages #17662

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25 changes: 14 additions & 11 deletions Lib/ast.py
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Original file line number Diff line number Diff line change
Expand Up @@ -62,20 +62,23 @@ 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):
def _raise_malformed_node(node, context = None):
message = "malformed node or string"
if context is not None and isinstance(node, AST):

iritkatriel Aug 22, 2020

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Why is it necessary to check here that node is an AST and not just that context is not None?

iritkatriel Aug 22, 2020

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I wonder if 'context' is overloaded. Maybe it's better not to add it here to the string passed in, and let the context arg be complete, like "literal expression" or "unary expression arg".

isidentical Aug 27, 2020

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Why is it necessary to check here that node is an AST and not just that context is not None?

For malformed nodes (manually constructed), it might not be an AST type, example (already presented in tests);

            ast.BinOp(
                ast.Constant(1), ast.Add(), "oops"
            ): "malformed node or string: 'oops'",

I wonder if 'context' is overloaded. Maybe it's better not to add it here to the string passed in, and let the context arg be complete, like "literal expression" or "unary expression arg".

I am not a native speaker, but from the point of messages, it satisfies the expectations and gives the precise location. (+a => ValueError: malformed node or string in binary operation context: <ast.Name object at 0x7f02f058d5f0>). What would you prefer instead of the message above? By the way thanks for your bump on this old PR! I completely forgot it existed since there was no activity :)

iritkatriel Aug 27, 2020

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  • I see about the first point.
  • On the wording - would it work to simply have "malformed binary operation" in this case?
  • My pleasure 👍
message += f" in {context} context"
raise ValueError(f'{message}: {node!r}')
def _convert_num(node, context):
if not isinstance(node, Constant) or type(node.value) not in (int, float, complex):
_raise_malformed_node(node)
_raise_malformed_node(node, context)
return node.value
def _convert_signed_num(node):
def _convert_signed_num(node, context):
if isinstance(node, UnaryOp) and isinstance(node.op, (UAdd, USub)):
operand = _convert_num(node.operand)
operand = _convert_num(node.operand, "unary operation")
if isinstance(node.op, UAdd):
return + operand
else:
return - operand
return _convert_num(node)
return _convert_num(node, context)
def _convert(node):
if isinstance(node, Constant):
return node.value
Expand All @@ -90,18 +93,18 @@ def _convert(node):
return set()
elif isinstance(node, Dict):
if len(node.keys) != len(node.values):
_raise_malformed_node(node)
_raise_malformed_node(node, "dictionary")
return dict(zip(map(_convert, node.keys),
map(_convert, node.values)))
elif isinstance(node, BinOp) and isinstance(node.op, (Add, Sub)):
left = _convert_signed_num(node.left)
right = _convert_num(node.right)
left = _convert_signed_num(node.left, "binary operation")
right = _convert_num(node.right, "binary operation")
if isinstance(left, (int, float)) and isinstance(right, complex):
if isinstance(node.op, Add):
return left + right
else:
return left - right
return _convert_signed_num(node)
return _convert_signed_num(node, "literal")
return _convert(node_or_string)


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16 changes: 16 additions & 0 deletions Lib/test/test_ast.py
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Expand Up @@ -971,6 +971,22 @@ def test_literal_eval_malformed_dict_nodes(self):
malformed = ast.Dict(keys=[ast.Constant(1)], values=[ast.Constant(2), ast.Constant(3)])
self.assertRaises(ValueError, ast.literal_eval, malformed)

def test_literal_eval_message(self):
tests = {
"2 * 5": "in literal context",
"[] + []": "in binary operation context",
"+''": "in unary operation context",
ast.Dict(
keys=[ast.Constant(1)], values=[]
): "in dictionary context",
ast.BinOp(
ast.Constant(1), ast.Add(), "oops"
): "malformed node or string: 'oops'",
}
for test, message in tests.items():
with self.subTest(test=test, expected_message=message):
self.assertRaisesRegex(ValueError, message, ast.literal_eval, test)

def test_bad_integer(self):
# issue13436: Bad error message with invalid numeric values
body = [ast.ImportFrom(module='time',
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5 changes: 4 additions & 1 deletion Lib/test/test_fstring.py
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Original file line number Diff line number Diff line change
Expand Up @@ -338,7 +338,10 @@ def g():
self.assertIsNone(g.__doc__)

def test_literal_eval(self):
with self.assertRaisesRegex(ValueError, 'malformed node or string'):
with self.assertRaisesRegex(
ValueError,
'malformed node or string in literal context'
):
ast.literal_eval("f'x'")

def test_ast_compile_time_concat(self):
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2019-12-19-18-20-08.bpo-32888.J5XUjV.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Enhance :func:`ast.literal_eval` error messages with context information. Original
patch is written by Chris Angelico, improved and maintained by Batuhan Taskaya.
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