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