[Tutor] exceptions problem

[bob gailer]

  On 9/11/2010 6:56 AM, Peter Otten wrote:
> Steven D'Aprano wrote:
>
>> On Sat, 11 Sep 2010 09:56:41 am bob gailer wrote:
>>>> I never thought that you can use a float and a integer to look if
>>>> the number is a integer.
>>> You can't.
>>
I made that comment in the context of the OPs function:

def readposint():
   x = raw_input("Please enter a positive integer :")
   try:
     if (int(x)<0 or (float(x) - int(x) > 0)): raise(ValueError)
   except:
     print x , "is not a positive integer. Try again."
     return -1
   return x

The OP thought (incorrectly) that, given for example:
x = '3.1'
float(x) - int(x) would evaluate to 0.1

In reality int(x) in this case raises an exception.
ValueError: invalid literal for int() with base 10: '3.1'

Since the expression was in a try he could not tell exactly what was 
happening.

I also don't quite understand the use of raise in the try.

I wish and hope that Roelof will learn how to do program walkthroughs 
and use the interactive prompt to solve things himself. I applaud the 
patience some of you have ih hand-holding him. I don't have that 
patience. I wish him to learn to fish.

-- 
Bob Gailer
919-636-4239
Chapel Hill NC