text: from jsonpickle.compat import PY32
  
  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 python2.6 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
          json_opts = ((), {'sort_keys': True})
          self._encoder_options = {
              'json': json_opts,
              'simplejson': json_opts,
              'django.util.simplejson': json_opts,
          }
  
          ## The exception class that is thrown when a decoding error occurs
          self._decoder_exceptions = {}
  
          ## Whether we've loaded any backends successfully
          self._verified = False
  
          if not PY32:
              self.load_backend('simplejson', 'dumps', 'loads', ValueError)
          self.load_backend('json', 'dumps', 'loads', ValueError)
          self.load_backend('demjson', 'encode', 'decode', 'JSONDecodeError')
          self.load_backend('jsonlib', 'write', 'read', 'ReadError')
          self.load_backend('yajl', 'dumps', 'loads', ValueError)
          self.load_backend('ujson', 'dumps', 'loads', ValueError)
  
      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, encode_name, decode_name, decode_exc):
          """
          Load a JSON backend by name.
  
          This method loads a backend and sets up references to that
          backend's encode/decode functions and exception classes.
  
          :param encode_name: is the name of the backend's encode method.
            The method should take an object and return a string.
          :param decode_name: names the backend's method for the reverse
            operation -- returning a Python object from a string.
          :param decode_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.
  
          """
          try:
              ## Load the JSON backend
              mod = __import__(name)
          except ImportError:
              return
  
          try:
              ## Handle submodules, e.g. django.utils.simplejson
              components = name.split('.')
              for comp in components[1:]:
                  mod = getattr(mod, comp)
          except AttributeError:
              return
  
          try:
              ## Setup the backend's encode/decode methods
              self._encoders[name] = getattr(mod, encode_name)
              self._decoders[name] = getattr(mod, decode_name)
          except AttributeError:
              self.remove_backend(name)
              return
  
          try:
              if type(decode_exc) is str:
                  ## This backend's decoder exception is part of the backend
                  self._decoder_exceptions[name] = getattr(mod, decode_exc)
              else:
                  ## simplejson uses the ValueError exception
                  self._decoder_exceptions[name] = decode_exc
          except AttributeError:
              self.remove_backend(name)
              return
  
          ## Setup the default args and kwargs for this encoder
          self._encoder_options[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
  
      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._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):
          """
          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)
  
          for idx, name in enumerate(self._backend_names):
              try:
                  optargs, optkwargs = self._encoder_options[name]
                  encoder_kwargs = optkwargs.copy()
                  encoder_args = (obj,) + tuple(optargs)
                  return self._encoders[name](*encoder_args, **encoder_kwargs)
              except Exception:
                  if idx == len(self._backend_names) - 1:
                      raise
  
      def backend_encode(self, name, obj):
          optargs, optkwargs = self._encoder_options[name]
          encoder_kwargs = optkwargs.copy()
          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 backend_decode(self, name, string):
          return self._decoders[name](string)
  
      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)
  