Newbie Python question about sys.argv

I'm currently going through a few tutorials to get myself up and running on Python, but I seem to hit the same problem a few times. The tutorial I'm currently following is Aloha.py in Introduction to Simulation by Norm Matloff.

The problem I'm hitting seems to be in the following code:

import random, sys
class node: # one object of this class models one network node
# some class variables
    s = int(sys.argv[1]) # number of nodes

The error message when I try and run the programme is:

Traceback (most recent call last):
  File "C:\Python26\Aloha.py", line 8, in <module>
    class node:
  File "C:\Python26\Aloha.py", lin开发者_JAVA技巧e 10, in node
    s = int(sys.argv[0])
ValueError: invalid literal for int() with base 10: 'C:\\Python26\\Aloha.py'

I've worked out that sys.argv[1] doesn't exist when I try and run the program, so does anyone know where I might be going wrong? Is there some way of starting the program that will set these values or is my system somehow set up incorrectly?

The traceback shows that you actually have this in your code:

s = int(sys.argv[0])

so you are referring to argument 0 - the script name itself - rather than 1.

sys.argv is for collecting the options given to the program on the command-line. So instead of just running the file, you'll want to run python aloha.py 5 (or whatever number you want).

(Otherwise, you could just set the number directly in the code instead of always expecting it on the command-line, as in s = 5 for example.)

Also, to load in command line arguments when you run a program you'd want to run your program like this...

python Aloha.py 75

Where 75 is replaced by the number of nodes. 75 will then become argv[1].

try

s = int(sys.argv[-1])