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
Related
So I was doing some python exercise and been stuck on one which teaches parameters, unpacking and variables so the code goes like this
from sys import argv
main.py, first, second, third = argv
print("The script is called:", main.py)
print("Your first variable is:", first)
print("Your second variable is:", second)
print("Your third variable is:", third)
but the error I get running this directly on compiler is
main.py, first, second, third = argv
ValueError: not enough values to unpack (expected 4, got 1)
Now if I run the code with terminal using command python3 main.py first second third as the book says I get the error
Traceback (most recent call last):
File "main.py", line 2, in <module>
main.py, first, second, third = argv
NameError: name 'main' is not defined
help would be appreciate
well, when you do:
main.py, first, second, third = argv
you expect to have always four argouments passed to oour file when started, but the Value Error is telling to you that only one has been passed.
Then the second error is raised because you use main.py to define a variable, but you can't use . in variable names, so simply turn your code in:
main, first, second, third = argv
then it should be adviceble to use some try: ... except: statement to handle errors in that part to avoid the brogram crashing when you pass the wrong number of arguments.
if you have a program that requires command line arguments like in that case you have always to start it with the arguments.
to avoid the first error you have to start the file like you do after in the question ,but will work only if you solve the second error.
import sys
try:
main, first, second, third = sys.argv
except ValueError:
first = input("first: ")
second = input("second: ")
third= input("third: ")
#main is the name of the file ,if you eant you can get it using __file__
in the above way you could avoid any error and if for any reason you start the file without passing any arguments, it will ask you them via shell.
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
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