[Tutor] exceptions problem

[bob gailer]

  On 9/10/2010 2:48 PM, Roelof Wobben wrote:
>
>
> Date: Fri, 10 Sep 2010 20:23:09 +0200
> From: fal at libero.it
> To: tutor at python.org
> Subject: Re: [Tutor] exceptions problem
>
> On 10/09/2010 18.12, Roelof Wobben wrote:
> >  ...
> >  def readposint():
> >          x = raw_input("Please enter a positive integer :")
> >          try:
> >                if not (x == int(x) and x<   0): raise(ValueError)
> >          except:
> >                  print x , "is not a positive integer.    Try again."
> >                  return False
> >          return True
> >
> >  y = readposint()
> >  print y
> >  while y == False:
> >          readposint()
> >  print "You have entered : ", y
> >
> >  But -9 and 2 are both true.
> My fault, I didn't notice that after raw_input, whatever you enter is a
> STRING, not an integer! So, without any exception thrown, the comparison
> x == int(x) is always False. Let's make it better:
>      if (int(x)<0 or (float(x) - int(x)>  0)): raise(ValueError)
>
>
> Then, if the input value x is indeed a positive integer, you should
> return x, not True or False. Try returning -1 if the exception is
> thrown, in line 7, and returning x in line 8. Then, you should change
> also line 12... ok, here's to you:
>
> 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
>
> y = readposint()
> print y
> while y == -1:
>       readposint()
> print "You have entered : ", y
>
> >
> >  Roelof
> Francesco
> Thank you.
> I never thought that you can use a float and a integer to look if the number is a integer.

You can't.


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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/tutor/attachments/20100910/6ced123f/attachment-0001.html>