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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 write_record(self, event_str):
 """Writes a serialized event to file."""

        header = struct.pack('Q', len(event_str))
        header += struct.pack('I', masked_crc32c(header))
        footer = struct.pack('I', masked_crc32c(event_str))
        self._writer.write(header + event_str + footer)