set object is not JSON serializable [duplicate]

Question

When I try to run the following code:

import json  d = {'testing': {1, 2, 3}} json_string = json.dumps(d) 

I get the following exception:

Traceback (most recent call last):   File "json_test.py", line 4, in <module>     json_string = json.dumps(d)   File "/usr/lib/python2.7/json/__init__.py", line 243, in dumps     return _default_encoder.encode(obj)   File "/usr/lib/python2.7/json/encoder.py", line 207, in encode     chunks = self.iterencode(o, _one_shot=True)   File "/usr/lib/python2.7/json/encoder.py", line 270, in iterencode     return _iterencode(o, 0)   File "/usr/lib/python2.7/json/encoder.py", line 184, in default     raise TypeError(repr(o) + " is not JSON serializable") TypeError: set([1, 2, 3]) is not JSON serializable 

What can I do to successfully use json.dumps with objects containing sets?

Answer 1

Turn sets into lists before serializing, or use a custom default handler to do so:

def set_default(obj):     if isinstance(obj, set):         return list(obj)     raise TypeError  result = json.dumps(yourdata, default=set_default) 

Answer 2

You can't fix it.

This error means just "json.dumps doesn't support data type "set".You should know JSON comes from javascript. And there is no data type like Python's "set" in javascript. So Python can't treat 'set' using JSON.

So you need another approach like @Martijn Pieters mentioned.

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UPDATE

I forgot to say this.

If you want to dump "set" or any other python object that is not supported JSON, you can use pickle or cPickle module. If you use the "dump.txt" only from Python, this may be helpful.

import cPickle  d = {'testing': {1, 2, 3}}  #dump with open("pickledump.txt", "w") as fp:     cPickle.dump(d, fp)  #load with open("pickledump.txt", "r") as fp:     x = cPickle.load(fp)