from functools import reduce

def pipeline(steps, initial=None):
    def apply(result, step):
        yield from step(result)
    
    yield from reduce(apply, steps, initial)

if __name__ == '__main__':
    # BEFORE
    before = notify(write(modify(sanitize(concat(read(FILES))))))
    
    # AFTER
    process = read, concat, sanitize, modify, write, notify
    after = pipeline(process, FILES)
    
    # alternate, BEFORE
    opened_files = read(FILES)
    meaningless_variable_name = concat(opened_files)
    etc = sanitize(meaningless_variable_name)
    step4 = modify(etc)
    step5 = write(step4)
    before = notify(step5)