<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def process_header(self, data):
 """ Reads the first part of the file to get some essential metadata # Returns return (dict):
 the metadata in the header """

        metadata = {
            "datacolumns": data.read_chunk("I"),
            "firstyear": data.read_chunk("I"),
            "lastyear": data.read_chunk("I"),
            "annualsteps": data.read_chunk("I"),
        }
        if metadata["annualsteps"] != 1:
            raise InvalidTemporalResError(
                "{}: Only annual files can currently be processed".format(self.filepath)
            )

        return metadata