I am not getting desired output of this program?
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)
How to use cmd to pass these arguments?
You call it like
python program.py a1 b2 c3
and it outputs
The script is called: /home/sophia/program.py
Your first variable is: a1
Your second variable is: b2
Your third variable is: c3
sys.argv contains list of strings, each corresponding to a command line parameter. First one is always the filename of the script; others are the optional parameters, ordered exactly as they were typed in a shell.
Note that the code you provided works correctly only when you pass exactly three parameters due to the tuple unpacking.
See the docs for sys.argv and also check out argparse module documentation if you are going to write a program handling lots of arguments.
Related
This question already has answers here:
Python Value Error: not enough values to unpack
(4 answers)
Closed 2 years ago.
I'm using Learning Python the Hard Way. In the process of my learning I came across this error. Though I have been trying to debug since yesterday, I couldn't.
This is my code:
import sys
from sys import argv
script, first, second = argv
print('the script is called:', script)
print('the first variable is:', first)
print('the second vriable is:', second)
print('the third variable is:', third)
The error you're getting means you're trying to deconstruct an iterable (list, tuple) into more values than there are in the actual list. If you were to run
print(argv, len(argv))
You might see that you don't have three variables in argv.
argv shows the parameters you provided while running a script. So for example, if I ran:
python test_args.py
I would only receive: ['test_args.py'] as my argv variable. If I tried providing more parameters, like:
python test_args.py a b
Then my argv would look like: ['test_args.py', 'a', 'b']. Your code is completely dependent on how many parameters are passed when you are running it, so mess around with that as well to get a better sense of what is going on.
I suppose that you are executing the script in this format
python script.py 10 20
The problem is that you are using an extra variable third which is not initialized.
If you really want 3 arguments, then you have to pass three values at execution time as follows.
python script.py 10 20 30
Then change the code as follows.
from sys import argv
script, first, second, third = argv
print('the script is called:', script)
print('the first variable is:', first)
print('the second vriable is:', second)
print('the third variable is:', third)
Thank you
I am getting valueError in this code.
I do not know why?
from sys import argv
(script,first,second,third)=argv
print('The script is called:',script)
print('The first variable is :',first)
print('The second variable is :',second)
print('The third variable is :',third)
You're either not providing enough arguments to run your script or providing too many arguments, you need to provide three arguments like this:
python3 script.py first second third
I'm practicing Python with the book called Learn "Python The Hard Way 3rd edition". I searched that this book is a good resource to get a start.
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)
And I got an error saying that value error: not enough values to unpack (expected 4, got 1).
You need to run the script with three arguments, so that argv contains four elements (the first is the script's name).
argv is a list containing the following:
argv[0] is the script pathname if known
argv[1], argv[2], argv[3]... contains arguments passed from the shell.
In order for your code to work you need to run it with 3 arguments so that they can be unpacked and assigned to your 4 variables.
Please help.
I am doing this exercise, but I am using jupiter to do the exercise. This is written for python 2
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 virable is:", third)
How do I write it correctecly in Python 3 . Thanks a lot!
This same example works in Python 3 as well.
```
>> python unpack.py 4 5 3
The script is called: unpack.py
Your first variable is 4
Your second variable is: 5
Your third virable is: 3
```
You can specify the arguments in such a way:
python arg1 arg2 ...
Same would work for Python3 as well, you don't need to change anything. But as a safe practice, do check for the arguments length. You don't want to crash your script. Good luck.
I'm running the code below in Spyder.
I have typed it in a py file and simply hit the run button.
When I try to run it I get the error:
ValueError: need more than 1 value to unpack
As shown here you are meant to give the inputs for the argv variable before running the program but I don't know how to do this is spyder?
http://learnpythonthehardway.org/book/ex13.html
from sys import argv
script, first, second, third = argv
print "The script is called:", script
print "The first variable is:", first
print "The second variable is:", second
print "Your third variable is:", third
To pass argv to a script in Spyder, you need to go the menu entry
Run > Configuration per file
or press the Ctrl+F6 key, then look for the option called
Command line options
on the dialog that appears after that, and finally enter the command line arguments you want to pass to the script, which in this case could be
one two three
In addition to configuring in the Run->Configure as explained in other answers,
you can use "runfile" directly from the console.
Run the following:
runfile('ex13.py', args='first second third')
In Spyder, go Run > Configure and define your argv values as showing in following diagram and to run the script just press F6
Read the FAQ at the bottom of the page, it specifically mentions this error.
Common Student Questions
Q. When I run it I get ValueError: need more than 1 value to unpack.
Remember that an important skill is paying attention to details. If you look at the What You Should See section you see that I run the script with parameters on the command line. You should replicate how I ran it exactly.
Make sure you run the command:
$ python ex13.py first 2nd 3rd
>> The script is called: ex13.py
>> Your first variable is: first
>> Your second variable is: 2nd
>> Your third variable is: 3rd
You can ensure that the arguments are supplied.
if __name__ == '__main__':
if len(argv) == 4:
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
else:
print 'You forgot the args...'