Question

I’m learning Python’s generator from this slide: http://www.dabeaz.com/generators/Generators.pdf
There is an example in it, which can be describe like this:
You have a log file called log.txt, write a program to watch the content of it, if there are new line added to it, print them. Two solutions:

1. with generator:  

    import time

    def follow(thefile):
        while True:
            line = thefile.readline()
            if not line:
                time.sleep(0.1)
                continue
            yield line

    logfile = open("log.txt")
    loglines = follow(logfile)
    for line in loglines:
        print line


2. Without generator:  

    import time

    logfile = open("log.txt")

    while True:
        line = logfile.readline()
        if not line:
            time.sleep(0.1)
            continue
        print line

What’s the benefit of using generator here?

Answer 1

If all you have is a hammer, everything looks like a nail

I’d almost just like to answer this question with just the above quote. Just because you can does not mean you need to all the time.

But conceptually the generator version separates functionality, the follow function serves the purpose of encapsulating the continuous reading from a file while waiting for new input. Which frees you to do anything in your loop with the new line that you want. In the second version the code to read from the file, and to print out is intermingled with the control loop. This might not be really an issue in this small example but that is something you might want to think about.