PyScripter - import argv error

Question

I am using "Learn Python the Hard Way" and using PyScripter for writing and running my code.

On Exercise 13 I have to make the following code run:

from sys import argv


script, first, second, third = argv

print "The script is called:", script
print "Your first variable is:", first
print "Your second variable is:", second
print "Your third variable is:", third

When I run it, I get an error saying

ValueError: need more than 1 value to unpack

I have read other questions about the same topic and can't seem to find an answer that works.

I am also quite new to coding so explaining how to do it would be great!

Answer 1

Your script will only work if you pass exactly three commandline arguments to it. For example:

script.py 1 2 3

You cannot use any other number of commandline arguments or else a ValueError will be raised.

Perhaps you should make your script a little more robust by checking how many arguments you received and then assigning the names first, second, and third appropriately.

Below is a demonstration:

from sys import argv, exit

argc = len(argv)  # Get the number of commandline arguments

if argc == 4:
    # There were 3 commandline arguments
    script, first, second, third = argv
elif argc == 3:
    # There were only 2 commandline arguments
    script, first, second = argv
    third = '3rd'
elif argc == 2:
    # There was only 1 commandline argument
    script, first = argv
    second = '2nd'
    third = '3rd'
elif argc == 1:
    # There was no commandline arguments
    script = argv[0]
    first = '1st'
    second = '2nd'
    third = '3rd'
else:
    print "Too many commandline arguments"
    exit(1)

print "The script is called:", script
print "Your first variable is:", first
print "Your second variable is:", second
print "Your third variable is:", third

Of course, this is just an example. You can do anything you want inside the if-statements (assign the names to something different, raise an exception, print a message, exit the script, etc.). The important part here is the argc = len(argv) line and the if-statements which check how many arguments the script received.