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.
Related
I'm trying to learn python by following book Named "learn python3 by hard way"
They gave this example of code.
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)
But in VS code pylint giving me this error.
Possible unbalanced tuple unpacking with sequence: left side has 4 label(s), right side has 0 value(s)
Book writer hadn't explained this and I want to know what does this error means
But they also said
Run the program like this (and you must pass three command line
arguments):
$ python3.6 ex13.py first 2nd 3rd
And how often python programmers use this method in practical world and any example of use-case.
The argument may not exactly be four. If it is less or more than 4, it may raise ValueError
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.
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'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.
The error is at script, first, second, third = argv. I would like to understand why I am getting the error and how to fix it.
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)
Run it from the shell like this:
python script.py arg1 arg2 arg3
argv variable contains command line arguments. In your code you expected 4 arguments, but got only 1 (first argument always script name). You could configure arguments in pycharm. Go to Run -> Edit Configurations. Then create a new python configuration. And there you could specify Script parameters field. Or you could run your script from command line as mentioned by dnit13.
You could run it like this: python script.py first, second, third
I think you are running the following command:
python script.py
You are writing a program which is aksing for 4 inputs and you are giving onle one. That's why you are receiving an error. You can use the below command:
python script.py Hello How Are