def METHOD_NAME(self):
    """Lazy function (generator) to read a sequence of files line by line."""
    for file in self.data_files:
        with open(file) as fp:
            for line in fp:
                line = line.rstrip().split()
                if len(line) == 0:
                    continue
                if line[0] in self.ignore_sras:  # already processed
                    print(f'{line[0]} is marked as already processed. Skipping...')
                    continue
                self.processed_sras += 1
                yield line
    return None