[Tutor] exceptions problem

[bob gailer]

  On 9/11/2010 12:12 PM, Roelof Wobben wrote:
>
>
> ----------------------------------------
>> Date: Sat, 11 Sep 2010 11:05:54 -0400
>> From: bgailer at gmail.com
>> To: tutor at python.org
>> Subject: Re: [Tutor] exceptions problem
>>
>> 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.
> Hello Bob,
>
> Oke, I try to  fish.

Thank you.

>
> When I do
>
> x= "a"
> y= int(x)
> Then I get ValueError.
>
> When I do
>
> x= 1.2
> y=int(x)
> No exception is raised.

As Dave pointed out you switched from string to numeric. Try instead x = 
'1.2'

> But when I do then x ==y I get a false.
> When I now do float(x) - int(x) I get 1.2 - 1 = 0.2 and that's greater then 0
>
> Because one of the two is true the Raise is executed.
>
>
> x = -9
> y=int(x)
> No exception is raised.
> X == y is True.
> But float(x) - int(x) I get 0.0 and 0.0>  0 is False.
> Because x == y is True the Raise is executed.
>
> Are these the right conclusions ??
>
> Roelof


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