blocks|key|731220|text|我想说的是，解析它是你真正完全了解它的唯一方法。如果格式不正确，python的json.loads()函数(几乎可以肯定)会引发异常。但是，根据示例的目的，您可能只需检查前几个非空格字符...|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|731221|我对facebook发回的JSON并不熟悉，但是大多数来自web应用的JSON字符串都会以一个开放的方形[或花括号{开头。据我所知，没有任何图像格式是以这些字符开头的。|731222|相反，如果您知道可能显示的图像格式，则可以检查字符串的开头是否有签名来识别图像，如果不是图像，则假定您有JSON。|731223|识别图形而不是文本字符串的另一个简单技巧是测试字符串的前几十个字符中是否有非ASCII字符(假设JSON是ASCII)。|731224|entityMap^0|13|C|0|1G|1|1L|1|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|V|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|W|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|M|$]]

I would say parsing it is the only way you can really entirely tell. Exception will be raised by python's <code>json.loads()</code> function (almost certainly) if not the correct format. However, the the purposes of your example you can probably just check the first couple of non-whitespace characters...

I'm not familiar with the JSON that facebook sends back, but most JSON strings from web apps will start with a open square <code>[</code> or curly <code>{</code> bracket. No images formats I know of start with those characters. 

Conversely if you know what image formats might show up, you can check the start of the string for their signatures to identify images, and assume you have JSON if it's not an image. 

Another simple hack to identify a graphic, rather than a text string, in the case you're looking for a graphic, is just to test for non-ASCII characters in the first couple of dozen characters of the string (assuming the JSON is ASCII).

blocks|key|731263|text|对于这个问题，我想出了一个通用的、有趣的解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|731264|class+SafeInvocator(object):
++++def+__init__(self,+module):
++++++++self._module+=+module

++++def+_safe(self,+func):
++++++++def+inner(*args,+**kwargs):
++++++++++++try:
++++++++++++++++return+func(*args,+**kwargs)
++++++++++++except:
++++++++++++++++return+None

++++++++return+inner

++++def+__getattr__(self,+item):
++++++++obj+=+getattr(self.module,+item)
++++++++return+self._safe(obj)+if+hasattr(obj,+'__call__')+else+obj|code-block|syntax|javascript|731265|你可以这样使用它：|731266|safe_json+=+SafeInvocator(json)
text+=+"{'foo':'bar'}"
item+=+safe_json.loads(text)
if+item:
++++#+do+something|731267|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I came up with an generic, interesting solution to this problem:

<pre><code>class SafeInvocator(object):
 def __init__(self, module):
 self._module = module

 def _safe(self, func):
 def inner(*args, **kwargs):
 try:
 return func(*args, **kwargs)
 except:
 return None

 return inner

 def __getattr__(self, item):
 obj = getattr(self.module, item)
 return self._safe(obj) if hasattr(obj, '__call__') else obj
</code></pre>

and you can use it like so:

<pre><code>safe_json = SafeInvocator(json)
text = "{'foo':'bar'}"
item = safe_json.loads(text)
if item:
 # do something
</code></pre>

blocks|key|731283|text|在try块中简单得多。然后，您可以验证主体是否为有效的JSON|type|unstyled|depth|inlineStyleRanges|entityRanges|data|731284|async+def+get_body(request:+Request):
try:
++++body+=+await+request.json()
except:
++++body+=+await+request.body()
return+body|code-block|syntax|javascript|731285|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Much simple in try block. You can then validate if the body is a valid JSON
<pre><code>async def get_body(request: Request):
try:
 body = await request.json()
except:
 body = await request.body()
return body
</code></pre>

In Python, is there a way to check if a string is valid JSON before trying to parse it? 

For example working with things like the Facebook Graph API, sometimes it returns JSON, sometimes it could return an image file.

How do I check if a string is valid JSON in Python?

Python

JSON

在Python中，有没有一种方法可以在解析字符串之前检查它是否是有效的JSON？例如，使用Facebook Graph API时，它有时会返回JSON，有时会返回图像文件。

问如何在Python中检查字符串是否为有效的JSON？
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