Using JSON keys as attributes in nested JSON - json

Question

I'm working with nested JSON-like data structures in python 2.7 that I exchange with some foreign perl code. I just want to 'work with' these nested structures of lists and dictionaries in amore pythonic way.
So if I have a structure like this...
a = {
'x': 4,
'y': [2, 3, { 'a': 55, 'b': 66 }],
}
...I want to be able to deal with it in a python script as if it was nested python classes/Structs, like this:
>>> aa = j2p(a) # <<- this is what I'm after.
>>> print aa.x
4
>>> aa.z = 99
>>> print a
{
'x': 4,
'y': [2, 3, { 'a': 55, 'b': 66 }],
'z': 99
}
>>> aa.y[2].b = 999
>>> print a
{
'x': 4,
'y': [2, 3, { 'a': 55, 'b': 999 }],
'z': 99
}
Thus aa is a proxy into the original structure. This is what I came up with so far, inspired by the excellent What is a metaclass in Python? question.
def j2p(x):
"""j2p creates a pythonic interface to nested arrays and
dictionaries, as returned by json readers.
>>> a = { 'x':[5,8], 'y':5}
>>> aa = j2p(a)
>>> aa.y=7
>>> print a
{'x': [5, 8], 'y':7}
>>> aa.x[1]=99
>>> print a
{'x': [5, 99], 'y':7}
>>> aa.x[0] = {'g':5, 'h':9}
>>> print a
{'x': [ {'g':5, 'h':9} , 99], 'y':7}
>>> print aa.x[0].g
5
"""
if isinstance(x, list):
return _list_proxy(x)
elif isinstance(x, dict):
return _dict_proxy(x)
else:
return x
class _list_proxy(object):
def __init__(self, proxied_list):
object.__setattr__(self, 'data', proxied_list)
def __getitem__(self, a):
return j2p(object.__getattribute__(self, 'data').__getitem__(a))
def __setitem__(self, a, v):
return object.__getattribute__(self, 'data').__setitem__(a, v)
class _dict_proxy(_list_proxy):
def __init__(self, proxied_dict):
_list_proxy.__init__(self, proxied_dict)
def __getattribute__(self, a):
return j2p(object.__getattribute__(self, 'data').__getitem__(a))
def __setattr__(self, a, v):
return object.__getattribute__(self, 'data').__setitem__(a, v)
def p2j(x):
"""p2j gives back the underlying json-ic json-ic nested
dictionary/list structure of an object or attribute created with
j2p.
"""
if isinstance(x, (_list_proxy, _dict_proxy)):
return object.__getattribute__(x, 'data')
else:
return x
Now I wonder whether there is an elegant way of mapping a whole set of the __*__ special functions, like __iter__, __delitem__? so I don't need to unwrap things using p2j() just to iterate or do other pythonic stuff.
# today:
for i in p2j(aa.y):
print i
# would like to...
for i in aa.y:
print i

Answer 1

I think you're making this more complex than it needs to be. If I understand you correctly, all you should need to do is this:
import json
class Struct(dict):
def __getattr__(self, name):
return self[name]
def __setattr__(self, name, value):
self[name] = value
def __delattr__(self, name):
del self[name]
j = '{"y": [2, 3, {"a": 55, "b": 66}], "x": 4}'
aa = json.loads(j, object_hook=Struct)
for i in aa.y:
print(i)
When you load JSON, the object_hook parameter lets you specify a callable object to process objects that it loads. I've just used it to turn the dict into an object that allows attribute access to its keys. Docs

Answer 2

There is an attrdict library that does exactly that in a very safe manner, but if you want, a quick and dirty (possibly leaking memory) approach was given in this answer:
class AttrDict(dict):
def __init__(self, *args, **kwargs):
super(AttrDict, self).__init__(*args, **kwargs)
self.__dict__ = self
j = '{"y": [2, 3, {"a": 55, "b": 66}], "x": 4}'
aa = json.loads(j, object_hook=AttrDict)

Answer 3

I found the answer: There is intentionally no way to automatically map the special methods in python, using __getattribute__. So to achieve what I want, I need to explicitely define all special methods like __len__ one after the other.