Help with my 8-year old son's first program. I'm stuck!

[justinpmullins at gmail.com]

Thanks Peter, that did the trick.
You've got here a very happy 8-year old and a mighty relieved 46-year old!!


On Saturday, January 25, 2014 10:41:20 AM UTC, Peter Otten wrote:
> justinpmullins at gmail.com wrote:
> 
> 
> 
> > My son is learning Python and I know nothing about computers.
> 
> > He's written a simple calculator program that doesn't work. 
> 
> 
> 
> Normally you are supposed to explain what you or your son expect and what 
> 
> you get instead. If Python ends with an error you should paste that into 
> 
> your message, e. g.:
> 
> 
> 
> Traceback (most recent call last):
> 
>   File "calculator.py", line 29, in <module>
> 
>     a()
> 
>   File "calculator.py", line 14, in a
> 
>     if op == str(d):
> 
> NameError: global name 'd' is not defined
> 
> 
> 
> Also, we need to know if you are using Python 2 or Python 3. Sometimes even 
> 
> the exact version is important. You can find it out with
> 
> 
> 
> $ python3 -V
> 
> Python 3.2.2
> 
> 
> 
> > For the life
> 
> > of me, I can't see why. Any help gratefully received. Here's his code:
> 
> 
> 
> > def a():
> 
> >         import sys
> 
> >         print("welcome to the calculation")
> 
> >         print("please type a number")
> 
> >         one = int(sys.stdin.readline())
> 
> >         print("type d for division,")
> 
> >         print("type m for multiplication,") 
> 
> >         print("type s for subtraction,")
> 
> >         print("and type p for plus")
> 
> >         op = (sys.stdin.readline())
> 
> >         print("%s selected" % op)
> 
> >         print("please enter another number")
> 
> >         two = int(sys.stdin.readline())
> 
> >         if op == str(d):
> 
> 
> 
> The name d is defined nowhere in your script. That line should be
> 
> 
> 
>           if op == "d":
> 
> 
> 
> similar to the `elif`s that follow.
> 
> 
> 
> >                 out == one / two
> 
> 
> 
> You want to assign to out but you are actually comparing out to one / two. 
> 
> Change the line (and similar lines below) to a single =, e. g.
> 
>                   out = one / two
> 
> 
> 
> >                 print("the answer is %s" % out)
> 
> >         elif op == "m":
> 
> >                 out == one * two
> 
> >                 print("the answer is %s" % out)
> 
> >         elif op == "s":
> 
> >                 out == one - two
> 
> >                 print("the answer is %s" % out)
> 
> >         elif op == "p":
> 
> >                 out == one + two
> 
> >                 print("the answer is %s" % out)
> 
> >         else:
> 
> >                 print("huh")
> 
> 
> 
> Change the above line to
> 
> 
> 
>                   print("Unknown op=%r" % op) 
> 
> 
> 
> and add a function invocation
> 
> 
> 
> a()
> 
> 
> 
> > Where is he going wrong?
> 
> > Many thanks in advance
> 
> 
> 
> When you run the script with my modifications
> 
> 
> 
> $ python3 calculator.py 
> 
> welcome to the calculation
> 
> please type a number
> 
> 10
> 
> type d for division,
> 
> type m for multiplication,
> 
> type s for subtraction,
> 
> and type p for plus
> 
> m
> 
> m
> 
>  selected
> 
> please enter another number
> 
> 20
> 
> Unknown op='m\n'
> 
> 
> 
> you see that what you supposed to be an "m" is actually an "m" followed by a 
> 
> newline. The readline() method reads a line including the final newline.
> 
> You can remove that by changing the line
> 
> 
> 
> op = (sys.stdin.readline())
> 
> 
> 
> to
> 
> 
> 
> op = sys.stdin.readline().strip()
> 
> 
> 
> but a more straightforward approach would be to replace all occurences of
> 
> 
> 
> sys.stdin.readline()
> 
> 
> 
> with 
> 
> 
> 
> input() # if you are using Python 3
> 
> 
> 
> or
> 
> 
> 
> raw_input() # if yo are using Python 2.