Preserve Python tuples with JSON

Question

I'm still a little new to this, so I might not know all the conventional terms for things:

Is it possible to preserve Python tuples when encoding with JSON? Right now json.loads(json.dumps(tuple)) gives me a list back. I don't want to convert my tuples to lists, but I want to use JSON. So, are there options?

The reason why: I'm creating an app that uses multi-dimensional arrays, not always the same shape. I've got some class methods that use recursion to probe the arrays and cast the endpoints as a string or int. I recently realized that (based on how my recursion works) I can use tuples to prevent deeper recursive searching of arrays (Python rawks). This could come in handy in situations where I know I for sure I won't need to be probing any deeper into my data structures.

Answer 1

You can write a highly-specialzed encoder and a decoder hook:

import json  class MultiDimensionalArrayEncoder(json.JSONEncoder):     def encode(self, obj):         def hint_tuples(item):             if isinstance(item, tuple):                 return {'__tuple__': True, 'items': item}             if isinstance(item, list):                 return [hint_tuples(e) for e in item]             if isinstance(item, dict):                 return {key: hint_tuples(value) for key, value in item.items()}             else:                 return item          return super(MultiDimensionalArrayEncoder, self).encode(hint_tuples(obj))  def hinted_tuple_hook(obj):     if '__tuple__' in obj:         return tuple(obj['items'])     else:         return obj   enc = MultiDimensionalArrayEncoder() jsonstring =  enc.encode([1, 2, (3, 4), [5, 6, (7, 8)]])  print jsonstring  # [1, 2, {"items": [3, 4], "__tuple__": true}, [5, 6, {"items": [7, 8], "__tuple__": true}]]  print json.loads(jsonstring, object_hook=hinted_tuple_hook)  # [1, 2, (3, 4), [5, 6, (7, 8)]] 

Answer 2

Nope, it's not possible. There is no concept of a tuple in the JSON format (see here for a concise breakdown of what types exist in JSON). Python's json module converts Python tuples to JSON lists because that's the closest thing in JSON to a tuple.

You haven't given much detail of your use case here, but if you need to store string representations of data structures that include tuples, a few possibilities immediately come to mind, which may or may not be appropriate depending upon your situation:

1. Create your own encoding and decoding functions
2. Use pickle (careful; pickle.loads isn't safe to use on user-provided input).
3. Use repr and ast.literal_eval instead of json.dumps and json.loads. repr will give you output reasonably similar in appearance to json.dumps, but repr will not convert tuples to lists. ast.literal_eval is a less powerful, more secure version of eval which will only decode strings, numbers, tuples, lists, dicts, booleans, and None.

Option 3 is probably the easiest and simplest solution for you.