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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(cls, data):
 """Create a header from a dictionary. Args: data: { "data_type": {}, //Type of data (e.g. Temperature) "unit": string, "analysis_period": {} // A Ladybug AnalysisPeriod "metadata": {}, // A dictionary of metadata } """

        # assign default values
        assert 'data_type' in data, 'Required keyword "data_type" is missing!'
        keys = ('data_type', 'unit', 'analysis_period', 'metadata')
        for key in keys:
            if key not in data:
                data[key] = None

        data_type = DataTypeBase.from_json(data['data_type'])
        ap = AnalysisPeriod.from_json(data['analysis_period'])
        return cls(data_type, data['unit'], ap, data['metadata'])