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hdjson.py
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hdjson.py
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#!/usr/bin/env python
# Copyright (c) 2011, Cornell University
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
# * Redistributions of source code must retain the above copyright notice,
# this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above copyright
# notice, this list of conditions and the following disclaimer in the
# documentation and/or other materials provided with the distribution.
# * Neither the name of HyperDex nor the names of its contributors may be
# used to endorse or promote products derived from this software without
# specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
# This work was inspired by Doug Hellman's article on JSON serialization of
# complex types located at http://www.doughellmann.com/PyMOTW/json/
import json
import inspect
import sys
# Use these parameters with encoder for human readable output, e.g.:
# hdjson.Encoder(**hdjson.HumanReadable).encode(obj)
HumanReadable = {'sort_keys':True, 'indent':2}
# Key types for dictionary normalization
KEYS_TUPLE, KEYS_INT = range(2)
class Encoder(json.JSONEncoder):
def default(self, obj):
# sets are not json serializable, need own handler
if isinstance(obj, set):
d = { '__class__':'set',
'__value__':list(obj)
}
return d
# all new-style classes are serialized into a dictionary
d = { '__class__':obj.__class__.__name__,
'__module__':obj.__module__,
}
d.update(obj.__dict__)
return d
def normalizeDictKeys(self, d, key_type):
# dict. with non-string keys must be normalized to strings
nd = {}
for key, value in d.iteritems():
if key_type == KEYS_TUPLE:
nkey = json.dumps(key)
elif key_type == KEYS_INT:
nkey = str(key)
else:
nkey = str(key)
nd[nkey] = value
return nd
class Decoder(json.JSONDecoder):
def __init__(self):
json.JSONDecoder.__init__(self, object_hook=self.dict_to_object)
def dict_to_object(self, d):
if '__class__' not in d:
return d
class_name = d.pop('__class__')
# some built in types need to be customer serialized too
if class_name == 'set':
return set(d['__value__'])
module_name = d.pop('__module__')
# __import returns top-level package when module name is in form
# package.module, need to lookup the actual module from sys
__import__(module_name)
module = sys.modules[module_name]
class_ = getattr(module, class_name)
# encode from unicode to ASCII
args = dict( (key.encode('ascii'), value) for key, value in d.items())
# inspect constructor for the object and only use the matching args
# allow for straight name or _name match
params = inspect.getargspec(getattr(class_, "__init__"))[0]
straight = dict((key, args[key]) for key in params if args.has_key(key))
stripped = dict((key, args['_'+key]) for key in params if args.has_key('_'+key))
pruned = dict(straight.items() + stripped.items())
inst = class_(**pruned)
return inst
def denormalizeDictKeys(self, d, key_type):
# decode dict. with non-string keys back to original format
nd = {}
for key, value in d.iteritems():
# not perfect, assumes the complex key was a tuple
if key_type == KEYS_TUPLE:
nkey = tuple(json.loads(key))
elif key_type == KEYS_INT:
nkey = int(key)
else:
nkey = str(key)
nd[nkey] = value
return nd