ValueError: too many values to unpack (expected 2)

Question

In the Python tutorial book I'm using, I typed an example given for simultaneous assignment. I get the aforementioned ValueError when I run the program, and can't figure out why.

Here's the code:

#avg2.py
#A simple program to average two exam scores
#Illustrates use of multiple input

def main():
    print("This program computes the average of two exam scores.")

    score1, score2 = input("Enter two scores separated by a comma: ")
    average = (int(score1) + int(score2)) / 2.0

    print("The average of the scores is:", average)

main()

Here's the output.

>>> import avg2
This program computes the average of two exam scores.
Enter two scores separated by a comma: 69, 87
Traceback (most recent call last):
  File "<pyshell#4>", line 1, in <module>
    import avg2
  File "C:\Python34\avg2.py", line 13, in <module>
    main()
  File "C:\Python34\avg2.py", line 8, in main
    score1, score2 = input("Enter two scores separated by a comma: ")
ValueError: too many values to unpack (expected 2)

Solution

The above code will work fine on Python 2.x. Because input behaves as raw_input followed by a eval on Python 2.x as documented here - https://docs.python.org/2/library/functions.html#input

However, above code throws the error you mentioned on Python 3.x. On Python 3.x you can use the ast module's literal_eval() method on the user input.

This is what I mean:

import ast

def main():
    print("This program computes the average of two exam scores.")

    score1, score2 = ast.literal_eval(input("Enter two scores separated by a comma: "))
    average = (int(score1) + int(score2)) / 2.0

    print("The average of the scores is:", average)

main()

Comments

[kindall]

Huh, never considered using literal_eval for that!