ValueError：使用ast.literal_eval的格式错误的字符串

Question

I'm doing a loop to get json api, here is what I have in my loop:

response_item = requests.request('GET',url_item,params=None,verify=False)
response_item = json.loads(response_item.text)
response_item = ast.literal_eval(json.dumps(response_item, ensure_ascii=False).encode('utf8'))

I scan around 45000 json objects, I generate "url_item" variable for each iteration. Each object is the same, I can get something like 7000 object and I have the following error when I reach the 7064th:

Traceback (most recent call last):
  File "C:\Python27\tools\api_item.py", line 47, in <module>
    response_item = ast.literal_eval(json.dumps(response_item, ensure_ascii=False).encode('utf8'))
  File "C:\Python27\lib\ast.py", line 80, in literal_eval
    return _convert(node_or_string)
  File "C:\Python27\lib\ast.py", line 63, in _convert
    in zip(node.keys, node.values))
  File "C:\Python27\lib\ast.py", line 62, in <genexpr>
    return dict((_convert(k), _convert(v)) for k, v
  File "C:\Python27\lib\ast.py", line 63, in _convert
    in zip(node.keys, node.values))
  File "C:\Python27\lib\ast.py", line 62, in <genexpr>
    return dict((_convert(k), _convert(v)) for k, v
  File "C:\Python27\lib\ast.py", line 79, in _convert
    raise ValueError('malformed string')
ValueError: malformed string

I used to print the second and third "response_item". Of course in this case the third one isn't displayed since I have the error just before, here what I have for the print after the json.load:

{u'restrictions': [], u'name': u'Sac \xe0 dos de base', u'level': 0, u'rarity': u'Basic', u'vendor_value': 11, u'details': {u'no_sell_or_sort': False, u'size': 20}, u'game_types': [u'Activity', u'Wvw', u'Dungeon', u'Pve'], u'flags': [u'NoSell', u'SoulbindOnAcquire', u'SoulBindOnUse'], u'icon': u'https://render.guildwars2.com/file/80E36806385691D4C0910817EF2A6C2006AEE353/61755.png', u'type': u'Bag', u'id': 8932, u'description': u'Un sac de 20 emplacements pour les personnages d\xe9butants.'}

Every item I get before this one has the same type, same format, and I don't have any error except for the 7064th !

Thank you for your help!

Answer 1

You should not use ast.literal_eval() on JSON data. JSON and Python literals may look like the same thing, but they are very much not.

In this case, your data contains a boolean flag, set to false in JSON. A proper Python boolean uses title-case, so False :

>>> import json, ast
>>> s = '{"no_sell_or_sort": false, "size": 20}'
>>> json.loads(s)
{u'no_sell_or_sort': False, u'size': 20}
>>> ast.literal_eval(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mj/Development/Library/buildout.python/parts/opt/lib/python2.7/ast.py", line 80, in literal_eval
    return _convert(node_or_string)
  File "/Users/mj/Development/Library/buildout.python/parts/opt/lib/python2.7/ast.py", line 63, in _convert
    in zip(node.keys, node.values))
  File "/Users/mj/Development/Library/buildout.python/parts/opt/lib/python2.7/ast.py", line 62, in <genexpr>
    return dict((_convert(k), _convert(v)) for k, v
  File "/Users/mj/Development/Library/buildout.python/parts/opt/lib/python2.7/ast.py", line 79, in _convert
    raise ValueError('malformed string')
ValueError: malformed string

Other differences include using null instead of None , and Unicode escape sequences in what to Python 2 looks like a plain (bytes) string , using UTF-16 surrogates when escaping non-BMP codepoints.

Load your data with json.loads() , not ast.literal_eval() . Not only will it handle proper JSON just fine, it is also faster .

In your case, it appears you are using json.dumps() then try to load the data again with ast.literal_eval() . There is no need for that step, you already had a Python object.

In other words, the line:

response_item = ast.literal_eval(json.dumps(response_item, ensure_ascii=False).encode('utf8'))

is redundant at best, and very, very wrong, at worst. Re-encoding response_item to a JSON string does not produce something that can be interpreted as a Python literal.

Answer 2

ast.literal_eval is safe with SQL injection if you are using this. because when an unwanted charter is inserted it will show Syntex error which prevents from an injection.