Decompress and concatenate .fastq files

def fileprep(self):
        """Decompress and concatenate .fastq files"""
        # Create and start threads
        for i in range(self.cpus):
            # Send the threads to the appropriate destination function
            threads = Thread(target=self.prep, args=())
            # Set the daemon to true - something to do with thread management
            threads.setDaemon(True)
            # Start the threading
            threads.start()
        for sample in self.metadata:
            # Set the name of the decompressed, combined .fastq file
            sample.general.combined = os.path.join(sample.general.outputdirectory, '{sample_name}_combined.fastq'
                                                   .format(sample_name=sample.name))
            self.queue.put(sample)
        self.queue.join()