gistfile1.py

    def concatenate(self, files, target, compress=False, progress=1):
        """
        Concatenate all the lines from files into the target.

        If compress is True, compress the file using gzip. Defaults to False.

        If progress is an integer, log an INFO message every N files (where
        N is the integer passed). Defaults to 1.

        Returns target.
        """
        if compress:
            opener = gzip.open
        else:
            opener = open

        count = len(files)
        self.logger.debug(
            'Concatenating %s input files to output file %r', count, target
        )
        with contextlib.closing(opener(target, 'w')) as tgt:
            for line in fileinput.input(files, mode='rb'):
                fname = fileinput.filename()
                index = files.index(fname)

                if fileinput.isfirstline():
                    self.logger.debug('Concatenating file: %r', fname)
                    if index % progress == 0:
                        self.logger.info('Processed %s/%s files.',
                                         index, count)

                tgt.write(line)

        return target