[Tutor] Problem with "input" in Python 3

Peter Anderson peter.anderson at internode.on.net
Mon Feb 15 13:09:23 CET 2010


I am trying to teach myself how to program in Python using Zelle's 
"Python Programming: An Introduction to Computer Science" (a very good 
text). At the same time I have decided to start with Python 3 (3.1.1). 
That means that I have to convert Zelle's example code to Python 3 
(which generally I cope with).

I'm hoping that somebody can help with what's probably a very simple 
problem. There is a quadratic equation example involving multiple user 
inputs from the one "input" statement. The code works fine with Python 
2.5 but when I convert it to Python 3 I get error messages. The code 
looks like:

05 import math
07 def main():
08 print("This program finds the real solutions to a quadratic\n")
10 a, b, c = input("Please enter the coefficients (a, b, c): ")
12 '''
13 a = int(input("Please enter the first coefficient: "))
14 b = int(input("Please enter the second coefficient: "))
15 c = int(input("Please enter the third coefficient: "))
16 '''
18 discrim = b * b - 4 * a * c
19 ...

25 main()

Lines 08 to 12 are my Python 3 working solution but line 06 does not 
work in Python 3. When it runs it produces:

Please enter the coefficients (a, b, c): 1,2,3
Traceback (most recent call last):
File "C:\Program Files\Wing IDE 101 3.2\src\debug\tserver\_sandbox.py", 
line 25, in <module>
File "C:\Program Files\Wing IDE 101 3.2\src\debug\tserver\_sandbox.py", 
line 10, in main
builtins.ValueError: too many values to unpack

Clearly the problem lies in the input statement. If I comment out line 
10 and remove the comments at lines 12 and 16 then the program runs 
perfectly. However, I feel this is a clumsy solution.

Could somebody please guide me on the correct use of "input" for 
multiple values.

*Peter Anderson*
There is nothing more difficult to take in hand, more perilous to 
conduct, or more uncertain in its success, than to take the lead in the 
introduction of a new order of things—Niccolo Machiavelli, /The Prince/, 
ch. 6

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