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43 changes: 43 additions & 0 deletions Doc/library/json.rst
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**Source code:** :source:`Lib/json/__init__.py`

.. testsetup:: *

import json
from json import AttrDict

--------------

`JSON (JavaScript Object Notation) <https://json.org>`_, specified by
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.. versionadded:: 3.5

.. class:: AttrDict(**kwargs)
AttrDict(mapping, **kwargs)
AttrDict(iterable, **kwargs)
Subclass of :class:`dict` object that also supports attribute style dotted access.

This class is intended for use with the :attr:`object_hook` in
:func:`json.load` and :func:`json.loads`::

.. doctest::

>>> json_string = '{"mercury": 88, "venus": 225, "earth": 365, "mars": 687}'
>>> orbital_period = json.loads(json_string, object_hook=AttrDict)
>>> orbital_period['earth'] # Dict style lookup
365
>>> orbital_period.earth # Attribute style lookup
365
>>> orbital_period.keys() # All dict methods are present
dict_keys(['mercury', 'venus', 'earth', 'mars'])

Attribute style access only works for keys that are valid attribute
names. In contrast, dictionary style access works for all keys. For
example, ``d.two words`` contains a space and is not syntactically
valid Python, so ``d["two words"]`` should be used instead.

If a key has the same name as a dictionary method, then a dictionary
lookup finds the key and an attribute lookup finds the method:

.. doctest::

>>> d = AttrDict(items=50)
>>> d['items'] # Lookup the key
50
>>> d.items() # Call the method
dict_items([('items', 50)])

.. versionadded:: 3.12


Standard Compliance and Interoperability
----------------------------------------
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52 changes: 51 additions & 1 deletion Lib/json/__init__.py
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Expand Up @@ -97,7 +97,7 @@
"""
__version__ = '2.0.9'
__all__ = [
'dump', 'dumps', 'load', 'loads',
'dump', 'dumps', 'load', 'loads', 'AttrDict',
'JSONDecoder', 'JSONDecodeError', 'JSONEncoder',
]

Expand Down Expand Up @@ -357,3 +357,53 @@ def loads(s, *, cls=None, object_hook=None, parse_float=None,
if parse_constant is not None:
kw['parse_constant'] = parse_constant
return cls(**kw).decode(s)

class AttrDict(dict):
"""Dict like object that supports attribute style dotted access.

This class is intended for use with the *object_hook* in json.loads():

>>> from json import loads, AttrDict
>>> json_string = '{"mercury": 88, "venus": 225, "earth": 365, "mars": 687}'
>>> orbital_period = loads(json_string, object_hook=AttrDict)
>>> orbital_period['earth'] # Dict style lookup
365
>>> orbital_period.earth # Attribute style lookup
365
>>> orbital_period.keys() # All dict methods are present
dict_keys(['mercury', 'venus', 'earth', 'mars'])

Attribute style access only works for keys that are valid attribute names.
In contrast, dictionary style access works for all keys.
For example, ``d.two words`` contains a space and is not syntactically
valid Python, so ``d["two words"]`` should be used instead.

If a key has the same name as dictionary method, then a dictionary
lookup finds the key and an attribute lookup finds the method:

>>> d = AttrDict(items=50)
>>> d['items'] # Lookup the key
50
>>> d.items() # Call the method
dict_items([('items', 50)])

"""
__slots__ = ()

def __getattr__(self, attr):
try:
return self[attr]
except KeyError:
raise AttributeError(attr) from None

def __setattr__(self, attr, value):
self[attr] = value

def __delattr__(self, attr):
try:
del self[attr]
except KeyError:
raise AttributeError(attr) from None

def __dir__(self):
return list(self) + dir(type(self))
1 change: 1 addition & 0 deletions Lib/test/test_json/__init__.py
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Expand Up @@ -18,6 +18,7 @@ class PyTest(unittest.TestCase):
json = pyjson
loads = staticmethod(pyjson.loads)
dumps = staticmethod(pyjson.dumps)
AttrDict = pyjson.AttrDict
JSONDecodeError = staticmethod(pyjson.JSONDecodeError)

@unittest.skipUnless(cjson, 'requires _json')
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145 changes: 145 additions & 0 deletions Lib/test/test_json/test_attrdict.py
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from test.test_json import PyTest
import pickle
import sys
import unittest

kepler_dict = {
"orbital_period": {
"mercury": 88,
"venus": 225,
"earth": 365,
"mars": 687,
"jupiter": 4331,
"saturn": 10_756,
"uranus": 30_687,
"neptune": 60_190,
},
"dist_from_sun": {
"mercury": 58,
"venus": 108,
"earth": 150,
"mars": 228,
"jupiter": 778,
"saturn": 1_400,
"uranus": 2_900,
"neptune": 4_500,
}
}

class TestAttrDict(PyTest):

def test_dict_subclass(self):
self.assertTrue(issubclass(self.AttrDict, dict))

def test_slots(self):
d = self.AttrDict(x=1, y=2)
with self.assertRaises(TypeError):
vars(d)

def test_constructor_signatures(self):
AttrDict = self.AttrDict
target = dict(x=1, y=2)
self.assertEqual(AttrDict(x=1, y=2), target) # kwargs
self.assertEqual(AttrDict(dict(x=1, y=2)), target) # mapping
self.assertEqual(AttrDict(dict(x=1, y=0), y=2), target) # mapping, kwargs
self.assertEqual(AttrDict([('x', 1), ('y', 2)]), target) # iterable
self.assertEqual(AttrDict([('x', 1), ('y', 0)], y=2), target) # iterable, kwargs

def test_getattr(self):
d = self.AttrDict(x=1, y=2)
self.assertEqual(d.x, 1)
with self.assertRaises(AttributeError):
d.z

def test_setattr(self):
d = self.AttrDict(x=1, y=2)
d.x = 3
d.z = 5
self.assertEqual(d, dict(x=3, y=2, z=5))

def test_delattr(self):
d = self.AttrDict(x=1, y=2)
del d.x
self.assertEqual(d, dict(y=2))
with self.assertRaises(AttributeError):
del d.z

def test_dir(self):
d = self.AttrDict(x=1, y=2)
self.assertTrue(set(dir(d)), set(dir(dict)).union({'x', 'y'}))

def test_repr(self):
# This repr is doesn't round-trip. It matches a regular dict.
# That seems to be the norm for AttrDict recipes being used
# in the wild. Also it supports the design concept that an
# AttrDict is just like a regular dict but has optional
# attribute style lookup.
self.assertEqual(repr(self.AttrDict(x=1, y=2)),
repr(dict(x=1, y=2)))

def test_overlapping_keys_and_methods(self):
d = self.AttrDict(items=50)
self.assertEqual(d['items'], 50)
self.assertEqual(d.items(), dict(d).items())

def test_invalid_attribute_names(self):
d = self.AttrDict({
'control': 'normal case',
'class': 'keyword',
'two words': 'contains space',
'hypen-ate': 'contains a hyphen'
})
self.assertEqual(d.control, dict(d)['control'])
self.assertEqual(d['class'], dict(d)['class'])
self.assertEqual(d['two words'], dict(d)['two words'])
self.assertEqual(d['hypen-ate'], dict(d)['hypen-ate'])

def test_object_hook_use_case(self):
AttrDict = self.AttrDict
json_string = self.dumps(kepler_dict)
kepler_ad = self.loads(json_string, object_hook=AttrDict)

self.assertEqual(kepler_ad, kepler_dict) # Match regular dict
self.assertIsInstance(kepler_ad, AttrDict) # Verify conversion
self.assertIsInstance(kepler_ad.orbital_period, AttrDict) # Nested

# Exercise dotted lookups
self.assertEqual(kepler_ad.orbital_period, kepler_dict['orbital_period'])
self.assertEqual(kepler_ad.orbital_period.earth,
kepler_dict['orbital_period']['earth'])
self.assertEqual(kepler_ad['orbital_period'].earth,
kepler_dict['orbital_period']['earth'])

# Dict style error handling and Attribute style error handling
with self.assertRaises(KeyError):
kepler_ad.orbital_period['pluto']
with self.assertRaises(AttributeError):
kepler_ad.orbital_period.Pluto

# Order preservation
self.assertEqual(list(kepler_ad.items()), list(kepler_dict.items()))
self.assertEqual(list(kepler_ad.orbital_period.items()),
list(kepler_dict['orbital_period'].items()))

# Round trip
self.assertEqual(self.dumps(kepler_ad), json_string)

def test_pickle(self):
AttrDict = self.AttrDict
json_string = self.dumps(kepler_dict)
kepler_ad = self.loads(json_string, object_hook=AttrDict)

# Pickling requires the cached module to be the real module
cached_module = sys.modules.get('json')
sys.modules['json'] = self.json
try:
for protocol in range(6):
kepler_ad2 = pickle.loads(pickle.dumps(kepler_ad, protocol))
self.assertEqual(kepler_ad2, kepler_ad)
self.assertEqual(type(kepler_ad2), AttrDict)
finally:
sys.modules['json'] = cached_module


if __name__ == "__main__":
unittest.main()
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Add AttrDict to JSON module for use with object_hook.