On 9/11/2010 12:12 PM, Roelof Wobben wrote:
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Date: Sat, 11 Sep 2010 11:05:54 -0400
From: bgai...@gmail.com
To: tutor@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
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