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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def from_json_file(cls, json_file):
 """Constructs a `GPT2Config` from a json file of parameters."""

        with open(json_file, "r", encoding="utf-8") as reader:
            text = reader.read()
        return cls.from_dict(json.loads(text))