Using arguments in python - value error

Question

I am new to python programming and I tried this code:

from sys import argv


script, first, second, third = argv
print "this script is called:" ,script

print "the first variable is called : " ,first

print "the second variable is called : ", second

print "the third variable is called : " ,third

I am getting the error :

Traceback (most recent call last):
  File "/Users/richavarma/Documents/first.py", line 4, in <module>
    script, first, second, third = argv
ValueError: need more than 1 value to unpack

My output should be as follows:

this script is called: abc.py
the first variable is called: first
the second variable is called : second
the third variable is called : third

Your program works on my end: python untitled.py 1 2 3 this script is called: untitled.py the first variable is called : 1 the second variable is called : 2 the third variable is called : 3 — rth
– rth, Commented May 21, 2017 at 3:54
My guess is that the error means you're not passing in any command line arguments. If I were you I would add a guard to check the number of arguments passed in to exit gracefully. Could you show us how you're executing your script? — Vaibhav Aggarwal
– Vaibhav Aggarwal, Commented May 21, 2017 at 3:54
@Richa that's the problem alright. sys.argv expects command line options. You can't do that from IDLE. Try running it from shell with command line args (like in rth's example) — Adam Smith
– Adam Smith, Commented May 21, 2017 at 4:03
Please post your terminal command line which return an error. Again on my side everything works. — rth
– rth, Commented May 21, 2017 at 4:38

fileyfood500 · Accepted Answer · 2017-05-21 05:51:44Z

1

In short, argv takes arguments from the command line. If you type this command into the command line:

python test.py first second third

You will pass 4 arguments to your python code: test.py, first, second, and third You can take in all 4 arguments as inputs by assignment like so:

from sys import argv

(filename, arg1, arg2, arg3) = argv

After this you can use any of the arguments as strings with their variable names.

answered May 21, 2017 at 5:51

fileyfood500

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