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

Question

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

User · Answer

Example Python script returns a boolean if a string is valid json:

import json

def is_json(myjson):
  try:
    json_object = json.loads(myjson)
  except ValueError as e:
    return False
  return True

Which prints:

print is_json("{}")                          #prints True
print is_json("{asdf}")                      #prints False
print is_json('{ "age":100}')                #prints True
print is_json("{'age':100 }")                #prints False
print is_json("{\"age\":100 }")              #prints True
print is_json('{"age":100 }')                #prints True
print is_json('{"foo":[5,6.8],"foo":"bar"}') #prints True

Convert a JSON string to a Python dictionary:

import json
mydict = json.loads('{"foo":"bar"}')
print(mydict['foo'])    #prints bar

mylist = json.loads("[5,6,7]")
print(mylist)
[5, 6, 7]

Convert a python object to JSON string:

foo = {}
foo['gummy'] = 'bear'
print(json.dumps(foo))           #prints {"gummy": "bear"}

If you want access to low-level parsing, don't roll your own, use an existing library: http://www.json.org/

Great tutorial on python JSON module: https://pymotw.com/2/json/

Is String JSON and show syntax errors and error messages:

sudo cpan JSON::XS
echo '{"foo":[5,6.8],"foo":"bar" bar}' > myjson.json
json_xs -t none < myjson.json

Prints:

, or } expected while parsing object/hash, at character offset 28 (before "bar}
at /usr/local/bin/json_xs line 183, <STDIN> line 1.

json_xs is capable of syntax checking, parsing, prittifying, encoding, decoding and more:

https://metacpan.org/pod/json_xs

User · Answer

You can try to do json loads    which will throw a ValueError if the string you pass can t be decoded as JSON   In general  the  Pythonic  philosophy for this kind of situation is called EAFP  for Easier to Ask for Forgiveness than Permission

User · Answer

I would say parsing it is the only way you can really entirely tell  Exception will be raised by python s json loads   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   or curly   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

User · Answer

I came up with an generic  interesting solution to this problem   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   and you can use it like so   safe json   SafeInvocator json  text      foo   bar    item   safe json loads text  if item        do something

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

Example Python script returns a boolean if a string is valid json:

Is String JSON and show syntax errors and error messages:

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