如何调试ast.literal_eval中的错误？ [英] How do I debug an error in `ast.literal_eval`?

问题描述

我使用 pprint.PrettyPrinter将数据写入文件 ，而我尝试使用 ast.literal_eval 。
这已经为我工作了一段时间了，我对所产生的文本表示形式感到满意。

I wrote my data to a file using pprint.PrettyPrinter and I am trying to read it using ast.literal_eval. This has been working for me for quite some time, and I am reasonably satisfied with the text representation produced.

但是，今天我在反序列化方面遇到了这个错误：

However, today I got this error on deserialization:

  File "/...mypath.../store.py", line 82, in <lambda>
    reader=(lambda fd: ast.literal_eval(fd.read())),
  File "/usr/lib64/python2.7/ast.py", line 80, in literal_eval
    return _convert(node_or_string)
  File "/usr/lib64/python2.7/ast.py", line 60, in _convert
    return list(map(_convert, node.elts))
  File "/usr/lib64/python2.7/ast.py", line 63, in _convert
    in zip(node.keys, node.values))
  File "/usr/lib64/python2.7/ast.py", line 62, in <genexpr>
    return dict((_convert(k), _convert(v)) for k, v
  File "/usr/lib64/python2.7/ast.py", line 63, in _convert
    in zip(node.keys, node.values))
  File "/usr/lib64/python2.7/ast.py", line 62, in <genexpr>
    return dict((_convert(k), _convert(v)) for k, v
  File "/usr/lib64/python2.7/ast.py", line 79, in _convert
    raise ValueError('malformed string')
ValueError: malformed string

如何修复

有问题的文件为17k行/ 700kb。
我将其加载到Emacs中-parens是平衡的。文件中没有非ASCII字符
我可以分割并征服（将文件切成两半，然后尝试对每一部分进行实数化）-但这很繁琐。
有什么更好的选择吗？

How do I fix this specific file?

The file in question is 17k lines/700kb. I loaded it into Emacs -- the parens are balanced. There are no non-ASCII characters in the file. I can "divide and conquer" (split the file in half and try to real each half) - but this is rather tedious. Is there anything better?

我修改了 ast.literal_eval：_convert 来打印有问题的节点-结果是< _ast.UnaryOp对象位于0x110696510> 。不是很有帮助。

I modified ast.literal_eval:_convert to print the offending node - it turned out to be <_ast.UnaryOp object at 0x110696510>. Not very helpful.

我希望 JSON 不是答案。;-）

I hope JSON is not the answer. ;-)

我没有使用 JSON ，因为

1. JSON无法处理非字符串字典键


2. JSON插入的换行过多或完全没有

1. JSON cannot handle non-string dict keys
2. JSON inserts either too many newlines or none at all

推荐答案

快速而肮脏

应用此补丁：

Quick and Dirty

Apply this patch:

--- /...../2.7/lib/python2.7/ast.py.old 2018-03-25 12:17:11.000000000 -0400
+++ /...../2.7/lib/python2.7/ast.py 2018-03-25 12:17:18.000000000 -0400
@@ -76,7 +76,7 @@ def literal_eval(node_or_string):
                 return left + right
             else:
                 return left - right
-        raise ValueError('malformed string')
+        raise ValueError('malformed string', node.lineno, node.col_offset)
     return _convert(node_or_string)

重新加载 ast ：

Reload ast:

>>> reload(ast)

重试加载有问题的文件

获取

Retry loading the offending file

Get

ValueError: ('malformed string', 21161, 10)

然后在第21161行的第10列是错误所在。

then line 21161, column 10 is where the error is.

将代码包装在 try / except ，捕获错误并使用 检查 / 追溯 来访问有问题的节点：

try:
    ast.literal_eval(...)
except ValueError as ex:
    _exc_type, exc_value, exc_traceback = sys.exc_info()
    print("ERROR: %r" % (exc_value))
    # traceback.print_tb(exc_traceback)
    last_tb = exc_traceback
    while last_tb.tb_next:
        last_tb = last_tb.tb_next
    print("Error location: line=%d, col=%d" % (
        last_tb.tb_frame.f_locals["node"].lineno,
        last_tb.tb_frame.f_locals["node"].col_offset))

打印

ERROR: ValueError('malformed string')
Error location: line=21933, col=15

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