<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def load_json(json_str):
 """Loads symbol from json string. Parameters json_str : str A JSON string. Returns ------- sym : Symbol The loaded symbol. See Also -------- Symbol.tojson : Used to save symbol into json string. """

    if not isinstance(json_str, string_types):
        raise TypeError('fname required to be string')
    handle = SymbolHandle()
    check_call(_LIB.MXSymbolCreateFromJSON(c_str(json_str), ctypes.byref(handle)))
    return Symbol(handle)