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Bug asking for input number

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  Bug asking for input number Arturo B <a7xrturodev@gmail.com> - 2013-11-15 18:15 -0800
    Re: Bug asking for input number MRAB <python@mrabarnett.plus.com> - 2013-11-16 02:33 +0000
    Re: Bug asking for input number Terry Reedy <tjreedy@udel.edu> - 2013-11-15 21:37 -0500
    Re: Bug asking for input number Arturo B <a7xrturodev@gmail.com> - 2013-11-15 19:03 -0800
    Re: Bug asking for input number Christopher Welborn <cjwelborn@live.com> - 2013-11-15 21:15 -0600
    Re: Bug asking for input number Christopher Welborn <cjwelborn@live.com> - 2013-11-15 20:47 -0600

#59582 — Bug asking for input number

Hi! I hope you can help me.

I'm writting a simple piece of code.
I need to keep asking for a number until it has all this specifications:

- It is a number
- It's lenght is 3
- The hundred's digit differs from the one's digit by at least two

My problem is that I enter a valid number like: 123, 321, 159, 346... and it keeps asking for a valid number.

Here's mi code:

res = input('Give me a number --> ')
hundreds = int(res[0])
ones = int(res[2])

# checks if the user enters a valid number
while not res.isdigit() or not len(res) == 3 or abs(hundreds - ones) <= 2:
    res = input('Enter a valid number --> ')

Thanks for help!

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#59583

On 16/11/2013 02:15, Arturo B wrote:
> Hi! I hope you can help me.
>
> I'm writting a simple piece of code.
> I need to keep asking for a number until it has all this specifications:
>
> - It is a number
> - It's lenght is 3
> - The hundred's digit differs from the one's digit by at least two
>
> My problem is that I enter a valid number like: 123, 321, 159, 346... and it keeps asking for a valid number.
>
> Here's mi code:
>
> res = input('Give me a number --> ')
> hundreds = int(res[0])
> ones = int(res[2])
>
> # checks if the user enters a valid number
> while not res.isdigit() or not len(res) == 3 or abs(hundreds - ones) <= 2:
>      res = input('Enter a valid number --> ')
>
> Thanks for help!
>
In the loop you're asking for the number but not doing the:

     hundreds = int(res[0])
     ones = int(res[2])

bit for it.

Also, after the number is entered for the first time, you're not
first checking its length or that it's a number.

It's probably easier just to use a break in a loop:

while True:
     res = input('Give me a number --> ')
     if len(res) == 3 and res.isdigit() and abs(int(res[0]) - 
int(res[2])) >= 2:
         break

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#59584

On 11/15/2013 9:15 PM, Arturo B wrote:
> Hi! I hope you can help me.
>
> I'm writting a simple piece of code.
> I need to keep asking for a number until it has all this specifications:
>
> - It is a number
> - It's lenght is 3
> - The hundred's digit differs from the one's digit by at least two
>
> My problem is that I enter a valid number like: 123, 321, 159, 346... and it keeps asking for a valid number.

If you enter a 'valid' number at first try, it works fine.

> Here's mi code:
>
> res = input('Give me a number --> ')
> hundreds = int(res[0])
> ones = int(res[2])
>
> # checks if the user enters a valid number
> while not res.isdigit() or not len(res) == 3 or abs(hundreds - ones) <= 2:

Look at that last condition *carefully*!!!!

>      res = input('Enter a valid number --> ')


-- 
Terry Jan Reedy

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#59585

MRAB your solution is good thank you I will use it.

Terry Eddy I saw my mistake about for example 2 <= 2, I think it's easier to use break in this case thank you!

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#59587

Sorry about my previous post, gmane is being really slow. :(

I wouldn't have posted if I knew the question was already answered.


-- 

- Christopher Welborn <cjwelborn@live.com>
   http://welbornprod.com

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#59588

On 11/15/2013 08:15 PM, Arturo B wrote:> Hi! I hope you can help me.
 >
 > I'm writting a simple piece of code.
 > I need to keep asking for a number until it has all this specifications:
 >
 > - It is a number
 > - It's lenght is 3
 > - The hundred's digit differs from the one's digit by at least two
 >
 > My problem is that I enter a valid number like: 123, 321, 159, 346... 
and it keeps asking for a valid number.
 >
 > Here's mi code:
 >
 > res = input('Give me a number --> ')
 > hundreds = int(res[0])
 > ones = int(res[2])
 >
 > # checks if the user enters a valid number
 > while not res.isdigit() or not len(res) == 3 or abs(hundreds - ones) 
<= 2:
 >      res = input('Enter a valid number --> ')
 >
 > Thanks for help!
 >


You only set 'hundreds' and 'ones' the first time, when the loop goes 
around those values never change. Also, I don't see any .isdigit() 
before you call int(), which may make it error (maybe you just didn't 
post the full code?). Also, I think your <= is flipped the wrong way.
The difference should be greater than or equal to 2 right?
Try something like this:

def is_valid_input(s):
     """ Returns True if a number is a digit,
         is 3 digits long,
         and hundreds - ones is >= 2
     """
     if not (s.isdigit() and (len(s) == 3)):
         return False
     hundreds = int(s[0])
     ones = int(s[2])
     return abs(hundreds - ones) >= 2

prompt = 'Give me a number --> '

res = input(prompt)
while not is_valid_input(res):
     print('\nInvalid number!: {}\n'.format(res))
     res = input(prompt)

...Of course you don't have to make it a function, I just did that 
because it was going to be used more than once. If you need to actually 
work with 'hundreds' and 'ones', you can rewrite it to suit your needs.

-- 

- Christopher Welborn <cjwelborn@live.com>
   http://welbornprod.com

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