[Tutor] Problem with "input" in Python 3

[Christian Witts]

pja wrote:
> Hi!
>
> 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
> 06
> 07 def main():
> 08 print("This program finds the real solutions to a quadratic\n")
> 09
> 10 a, b, c = input("Please enter the coefficients (a, b, c): ")
> 11
> 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 '''
> 17
> 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.
>
> Regards,
> Peter
You will need to split your input.

no_input = True
while no_input:
    in = input("Please enter the coefficients (a, b, c): ")
    try:
        a, b, c = map(int, in.split(','))
        no_input = False
    except ValueError:
        print("Please enter your input in a comma-seperated format with 
no space.  Only 3 numbers allowed")

That will loop allowing input until the person enters 3 numbers 
seperated purely by commas in for input.

-- 
Kind Regards,
Christian Witts
Business Intelligence

C o m p u s c a n | Confidence in Credit

Telephone: +27 21 888 6000
National Cell Centre: 0861 51 41 31
Fax: +27 21 413 2424
E-mail: cwitts at compuscan.co.za

NOTE:  This e-mail (including attachments )is subject to the disclaimer published at: http://www.compuscan.co.za/live/content.php?Item_ID=494.
If you cannot access the disclaimer, request it from email.disclaimer at compuscan.co.za or 0861 514131.

National Credit Regulator Credit Bureau Registration No. NCRCB6