sys.exit()

[IHeart SymLinks]

I am reading http://learnpythonthehardway.com/ and in one of the scripts he does a from sys import exit

What is the difference between exit and sys.exit()

The script appears to work fine without the import, so why did he import it?

[SGSeries2]

Lol, it seems like you really are trying to learn the hard way. You've racked up as many posts here since the beginning of the year as I've posted since I joined. (But, then again, a lot of people have out-posted me, so I supposed that doesn't really say much.)

Anyways, to answer you question (and you've probably already figured this out).

When you use "from x import y" to import something, you're bringing y from module x into your local namespace, so when you say "from sys import exit", exit() is brought into your local namespace and can be called without using the module name first, like sys.exit(). So, the two both point to the same thing in the end.

I'd have to see the code as to why the import is there, but he likely made the import for later convenience, but maybe didn't use it (imported out of habit, perhaps), or testing never went down that path of execution where it would fail without the import. (Dynamic languages let you do that.) You don't absolutely have to call exit, but it is nice, and useful if you want your program to tell the caller something went wrong.

On importing (from a google search):
http://effbot.org/zone/import-confusion.htm

[IHeart SymLinks]

Originally Posted by SGSeries2

Lol, it seems like you really are trying to learn the hard way.

What do you mean by that?

Here is the code for one of the exercises:

from sys import exit

def gold_room():
    print "This room is full of gold.How much do you take?"

    next = raw_input("> ")
    if "0" in next or "1" in next:
        how_much = int(next)
    else:
        dead("Man, learn to type a number.")

    if how_much < 50:
        print "Nice, you're not greedy, you win!"
        exit(0)
    else:
        dead("You greedy bastard!")


def bear_room():
    print "There is a bear here."
    print "The bear has a bunch of honey."
    print "The fat bear is in front of another door."
    print "How are you going to move the bear?"
    bear_moved = False

    while True:
        next = raw_input("> ")

        if next == "take honey":
            dead("The bear looks at you then pimp slaps your face off.")
        elif next == "taunt bear" and not bear_moved:
            print "The bear has moved from the door. You can go through it now."
            bear_moved = True
        elif next == "taunt bear" and bear_moved:
            dead("The bear gets pissed off and chews your crotch off.")
        elif next == "open door" and bear_moved:
            gold_room()
        else:
            print "I got no idea what that means."


def cthulu_room():
    print "Here you see the great evil Cthulu."
    print "He, it, whatever stares at you and you go insane."
    print "Do you flee for your life or eat your head?"

    next = raw_input("> ")

    if "flee" in next:
        start()
    elif "head" in next:
        dead("Well that was tasty!")
    else:
        cthulu_room()


def dead(why):
    print why, "Good job!"
    exit(0)

def start():
    print "You are in a dark room."
    print "There is a door to your right and left."
    print "Which one do you take?"

    next = raw_input("> ")

    if next == "left":
        bear_room()
    elif next == "right":
        cthulu_room()
    else:
        dead("You stumble around the room until you starve.")


start()

He uses exit to end the program after the player wins the game or dies.

Funny thing is the program behaves the same way without the import. I like to use quit (same thing as exit?) when I have code I want to test. So for example if I have this file:

Here is code I already am working on

and I want to test this code

Code to test

Then I would simply add the code at the top and put in quit so it looks like:

Code to test





quit()
Here is code I already am working on

That way I can test the code without having to make a new file or delete the contents of my existing file and when I am done I just remove the test code and quit() statement.

But perhaps he imported it to get the reader used to the idea of importing. He didn't have to but made the reader do it anyways.

[SGSeries2]

Originally Posted by IHeart SymLinks

What do you mean by that?

Oh, I was just playing with the website's name. Nothing more, really.

Originally Posted by IHeart SymLinks

Here is the code for one of the exercises:

... snip ...

That is interesting. I can't say I've used quit() or exit() that way (the automatic import versions, which are used if you comment out the import statement). Apparently exit and quit are constants that are automatically imported from the site module on initialization.

http://docs.python.org/library/constants.html#exit

And back in python 2.4, there were differences between the two (site & sys exit()s), but not anymore (I started using python post 2.5 release):
http://groups.google.com/group/comp....318b07030a048/

Like the docs say, the site module can be suppressed, and particularly the note on site's quit & exit (along with the other constants) may be of interest: "They are useful for the interactive interpreter shell and should not be used in programs." So I'd suggest sticking with sys.exit().

I know I learned something today.