<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def from_json(cls, string):
 """Create a ChemicalEntity from a json string """

        exp_dict = json_to_data(string)
        version = exp_dict.get('version', 0)
        if version == 0:
            return cls.from_dict(exp_dict)
        elif version == 1:
            return cls.from_dict(exp_dict)
        else:
            raise ValueError("Version %d not supported" % version)