JSON serialize a dictionary with tuples as key

Question

Is there a way in Python to serialize a dictionary that is using a tuple as key?

e.g.

a = {(1, 2): 'a'} 

simply using json.dumps(a) raises this error:

Traceback (most recent call last):   File "<stdin>", line 1, in <module>   File "/usr/lib/python2.6/json/__init__.py", line 230, in dumps     return _default_encoder.encode(obj)   File "/usr/lib/python2.6/json/encoder.py", line 367, in encode     chunks = list(self.iterencode(o))   File "/usr/lib/python2.6/json/encoder.py", line 309, in _iterencode     for chunk in self._iterencode_dict(o, markers):   File "/usr/lib/python2.6/json/encoder.py", line 268, in _iterencode_dict     raise TypeError("key {0!r} is not a string".format(key)) TypeError: key (1, 2) is not a string 

Answer 1

You can't serialize that as json, json has a much less flexible idea about what counts as a dict key than python.

You could transform the mapping into a sequence of key, value pairs, something like this:

import json def remap_keys(mapping):     return [{'key':k, 'value': v} for k, v in mapping.iteritems()] ...  json.dumps(remap_keys({(1, 2): 'foo'})) >>> '[{"value": "foo", "key": [1, 2]}]' 

Answer 2

from json import loads, dumps from ast import literal_eval  x = {(0, 1): 'la-la la', (0, 2): 'extricate'}  # save: convert each tuple key to a string before saving as json object s = dumps({str(k): v for k, v in x.items()})  # load in two stages: # (i) load json object obj = loads(s)  # (ii) convert loaded keys from string back to tuple d = {literal_eval(k): v for k, v in obj.items()} 

See https://stackoverflow.com/a/12337657/2455413.