from __future__ import absolute_import, division, unicode_literals
from .compat import string_types
from .compat import PY3_ORDERED_DICT
class JSONBackend(object):
"""Manages encoding and decoding using various backends.
It tries these modules in this order:
simplejson, json, demjson
simplejson is a fast and popular backend and is tried first.
json comes with Python and is tried second.
demjson is the most permissive backend and is tried last.
"""
def __init__(self, fallthrough=True):
# Whether we should fallthrough to the next backend
self._fallthrough = fallthrough
# The names of backends that have been successfully imported
self._backend_names = []
# A dictionary mapping backend names to encode/decode functions
self._encoders = {}
self._decoders = {}
# Options to pass to specific encoders
self._encoder_options = {}
# Options to pass to specific decoders
self._decoder_options = {}
# The exception class that is thrown when a decoding error occurs
self._decoder_exceptions = {}
# Whether we've loaded any backends successfully
self._verified = False
self.load_backend('simplejson')
self.load_backend('json')
self.load_backend('demjson', 'encode', 'decode', 'JSONDecodeError')
self.load_backend('jsonlib', 'write', 'read', 'ReadError')
self.load_backend('yajl')
self.load_backend('ujson')
# Defaults for various encoders
sort = not PY3_ORDERED_DICT
json_opts = ((), {'sort_keys': sort})
self._encoder_options = {
'ujson': ((), {'sort_keys': sort, 'escape_forward_slashes': False}),
'json': json_opts,
'simplejson': json_opts,
'django.util.simplejson': json_opts,
}
def _verify(self):
"""Ensures that we've loaded at least one JSON backend."""
if self._verified:
return
raise AssertionError(
'jsonpickle requires at least one of the '
'following:\n'
' python2.6, simplejson, or demjson'
)
def enable_fallthrough(self, enable):
"""
Disable jsonpickle's fallthrough-on-error behavior
By default, jsonpickle tries the next backend when decoding or
encoding using a backend fails.
This can make it difficult to force jsonpickle to use a specific
backend, and catch errors, because the error will be suppressed and
may not be raised by the subsequent backend.
Calling `enable_backend(False)` will make jsonpickle immediately
re-raise any exceptions raised by the backends.
"""
self._fallthrough = enable
def load_backend(self, name, dumps='dumps', loads='loads', loads_exc=ValueError):
"""Load a JSON backend by name.
This method loads a backend and sets up references to that
backend's loads/dumps functions and exception classes.
:param dumps: is the name of the backend's encode method.
The method should take an object and return a string.
Defaults to 'dumps'.
:param loads: names the backend's method for the reverse
operation -- returning a Python object from a string.
:param loads_exc: can be either the name of the exception class
used to denote decoding errors, or it can be a direct reference
to the appropriate exception class itself. If it is a name,
then the assumption is that an exception class of that name
can be found in the backend module's namespace.
:param load: names the backend's 'load' method.
:param dump: names the backend's 'dump' method.
:rtype bool: True on success, False if the backend could not be loaded.
"""
try:
# Load the JSON backend
mod = __import__(name)
except ImportError:
return False
# Handle submodules, e.g. django.utils.simplejson
try:
for attr in name.split('.')[1:]:
mod = getattr(mod, attr)
except AttributeError:
return False
if not self._store(self._encoders, name, mod, dumps) or not self._store(
self._decoders, name, mod, loads
):
return False
if isinstance(loads_exc, string_types):
# This backend's decoder exception is part of the backend
if not self._store(self._decoder_exceptions, name, mod, loads_exc):
return False
else:
# simplejson uses ValueError
self._decoder_exceptions[name] = loads_exc
# Setup the default args and kwargs for this encoder/decoder
self._encoder_options.setdefault(name, ([], {}))
self._decoder_options.setdefault(name, ([], {}))
# Add this backend to the list of candidate backends
self._backend_names.append(name)
# Indicate that we successfully loaded a JSON backend
self._verified = True
return True
def remove_backend(self, name):
"""Remove all entries for a particular backend."""
self._encoders.pop(name, None)
self._decoders.pop(name, None)
self._decoder_exceptions.pop(name, None)
self._decoder_options.pop(name, None)
self._encoder_options.pop(name, None)
if name in self._backend_names:
self._backend_names.remove(name)
self._verified = bool(self._backend_names)
def encode(self, obj, indent=None, separators=None):
"""
Attempt to encode an object into JSON.
This tries the loaded backends in order and passes along the last
exception if no backend is able to encode the object.
"""
self._verify()
if not self._fallthrough:
name = self._backend_names[0]
return self.backend_encode(name, obj, indent=indent, separators=separators)
for idx, name in enumerate(self._backend_names):
try:
return self.backend_encode(
name, obj, indent=indent, separators=separators
)
except Exception as e:
if idx == len(self._backend_names) - 1:
raise e
# def dumps
dumps = encode
def backend_encode(self, name, obj, indent=None, separators=None):
optargs, optkwargs = self._encoder_options.get(name, ([], {}))
encoder_kwargs = optkwargs.copy()
if indent is not None:
encoder_kwargs['indent'] = indent
if separators is not None:
encoder_kwargs['separators'] = separators
encoder_args = (obj,) + tuple(optargs)
return self._encoders[name](*encoder_args, **encoder_kwargs)
def decode(self, string):
"""
Attempt to decode an object from a JSON string.
This tries the loaded backends in order and passes along the last
exception if no backends are able to decode the string.
"""
self._verify()
if not self._fallthrough:
name = self._backend_names[0]
return self.backend_decode(name, string)
for idx, name in enumerate(self._backend_names):
try:
return self.backend_decode(name, string)
except self._decoder_exceptions[name] as e:
if idx == len(self._backend_names) - 1:
raise e
else:
pass # and try a more forgiving encoder, e.g. demjson
# def loads
loads = decode
def backend_decode(self, name, string):
optargs, optkwargs = self._decoder_options.get(name, ((), {}))
decoder_kwargs = optkwargs.copy()
return self._decoders[name](string, *optargs, **decoder_kwargs)
def set_preferred_backend(self, name):
"""
Set the preferred json backend.
If a preferred backend is set then jsonpickle tries to use it
before any other backend.
For example::
set_preferred_backend('simplejson')
If the backend is not one of the built-in jsonpickle backends
(json/simplejson, or demjson) then you must load the backend
prior to calling set_preferred_backend.
AssertionError is raised if the backend has not been loaded.
"""
if name in self._backend_names:
self._backend_names.remove(name)
self._backend_names.insert(0, name)
else:
errmsg = 'The "%s" backend has not been loaded.' % name
raise AssertionError(errmsg)
def set_encoder_options(self, name, *args, **kwargs):
"""
Associate encoder-specific options with an encoder.
After calling set_encoder_options, any calls to jsonpickle's
encode method will pass the supplied args and kwargs along to
the appropriate backend's encode method.
For example::
set_encoder_options('simplejson', sort_keys=True, indent=4)
set_encoder_options('demjson', compactly=False)
See the appropriate encoder's documentation for details about
the supported arguments and keyword arguments.
"""
self._encoder_options[name] = (args, kwargs)
def set_decoder_options(self, name, *args, **kwargs):
"""
Associate decoder-specific options with a decoder.
After calling set_decoder_options, any calls to jsonpickle's
decode method will pass the supplied args and kwargs along to
the appropriate backend's decode method.
For example::
set_decoder_options('simplejson', encoding='utf8', cls=JSONDecoder)
set_decoder_options('demjson', strict=True)
See the appropriate decoder's documentation for details about
the supported arguments and keyword arguments.
"""
self._decoder_options[name] = (args, kwargs)
def _store(self, dct, backend, obj, name):
try:
dct[backend] = getattr(obj, name)
except AttributeError:
self.remove_backend(backend)
return False
return True
json = JSONBackend()