<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set(self, key, value):
 """ Sets a single value in a preconfigured data file. Arguments: key -- The full dot-notated key to set the value for. value -- The value to set. """

        d = self.data.data
        keys = key.split('.')
        latest = keys.pop()
        for k in keys:
            d = d.setdefault(k, {})

        schema = Schema().load(self.schema_file)

        self.data.internal = schema.internal
        self.parse_value(d, '', key, value, schema.get(key))
        self.data.save(self.data_file)