def load(self, callables_fname):
        r"""
        Load traced modules information from a `JSON <http://www.json.org/>`_ file.

        The loaded module information is merged with any existing module information

        :param callables_fname: File name
        :type  callables_fname: :ref:`FileNameExists`

        :raises:
         * OSError (File *[fname]* could not be found)

         * RuntimeError (Argument \\`callables_fname\\` is not valid)
        """
        # Validate file name
        _validate_fname(callables_fname)
        if not os.path.exists(callables_fname):
            raise OSError("File {0} could not be found".format(callables_fname))
        with open(callables_fname, "r") as fobj:
            fdict = json.load(fobj)
        if sys.hexversion < 0x03000000:  # pragma: no cover
            fdict = _unicode_to_ascii(fdict)
        self._callables_db.update(fdict["_callables_db"])
        # Reverse the tuple-to-string conversion that the save method
        # does due to the fact that JSON keys need to be strings and the
        # keys of the reverse callable dictionary are tuples where the first
        # item is a file name and the second item is the starting line of the
        # callable within that file (dictionary value)
        rdict = {}
        for key, value in fdict["_reverse_callables_db"].items():
            tokens = key[1:-1].split(",")
            key = tokens[0].strip()[1:-1]
            if platform.system().lower() == "windows":  # pragma: no cover
                while True:
                    tmp = key
                    key = key.replace("\\\\", "\\")
                    if tmp == key:
                        break
            rdict[(key, int(tokens[1]))] = value
        self._reverse_callables_db.update(rdict)
        self._modules_dict.update(fdict["_modules_dict"])
        self._fnames.update(fdict["_fnames"])
        self._module_names.extend(fdict["_module_names"])
        self._class_names.extend(fdict["_class_names"])
        self._module_names = sorted(list(set(self._module_names)))
        self._class_names = sorted(list(set(self._class_names)))