frustrated stupid newbie question

[Joshua Macy]

Scott Kurland wrote:

>>>>>Why isn't this $%^*#$% program working?
>>>>>
>>>>>#Searching for perfect numbers
>>>>>
>>>>>howhigh= input ("How high should I check?")
>>>>>for number in range (1,howhigh):
>>>>> factorsum = 0
>>>>> halfnumber=number/2
>>>>> for checking in range (1,halfnumber):
>>>>>  if number/checking == int (number/checking):
>>>>>   factorsum = factorsum + checking
>>>>> if number == factorsum:
>>>>>  print number
>>>>>
>>>>>
>>>Well, I was expecting failure, which we got.  What I hoped for was the
>>>
> two
> 
>>>perfect numbers between 1 and 50, 6 and 28.

   As others pointed out, you're being bitten both by integer division 
and range not extending as high as you thought.  Change the 2 to 2.0 to 
force floating point in the division, add 1 to each of the end ranges, 
and use the modulo operator to do the comparison and it works:

howhigh= input ("How high should I check?")
for number in range (1,howhigh + 1):
     factorsum = 0
     halfnumber=number / 2.0
     for checking in range (1, halfnumber + 1):
         if number % checking == 0:
             factorsum = factorsum + checking
     if number == factorsum:
         print number


How high should I check?50
6
28

On recent releases of Python (2.1+, I believe) you can also add the line:

from __future__ import division

to your program, which will make division behave the way you were expecting.