[Tutor] Python program malfunction

[Alan Gauld]

On 04/05/15 05:26, Jag Sherrington wrote:
> Hi,
> There appears to be a problem with this program.
> It is taken from the "Starting out with Python" book third edition.
>
> The problem is when the "validate the wholesale cost" is introduced.
> Without the validator the code works fine, but with it the code won't let you enter a positive wholesale cost unless you do a negative cost first.
> Even after you have entered a negative cost and got the results of your positive cost it asks wether you want to do another item if you type "y" you still can't enter a positive amount.
>
> HERE IS THE CODE AS COPIED FROM THE BOOK:
>
> #This program calculates retail prices.
>
> mark_up = 2.5  # The mark up percentage.
> another = 'y'   # Variable to control the loop.
>
> # Process one or more items.
> while another == 'y' or another == 'y':

That's the same test twice. Is that what you meant?

>      #Get the item 's wholesale cost'
>      wholesale = float(input("Enter the item's wholesale cost: "))
>
>      # Validate the wholesale cost.
>      while wholesale < 0:
>          print('ERROR: the cost cannot be negative.')
>          wholesale = float(input('Enter the correct wholesale cost: '))
>
>          #Calculate the retail price.
>          retail = wholesale * mark_up
>
>          #Display the retail price.
>          print('Retail price: $', format(retail, ',.2f'), sep='')
>
>          #Do this again.
>          another = input('Do you have another item? ' + \
>                          '(Enter y for yes): ')
>
> HERE ARE THE RESULTS:
>
> Enter the item's wholesale cost: 0.50
> Enter the item's wholesale cost:    (THIS SEEMS TO BE A PROBLEM)

No problem, its exactly what your program tells it to do.
If the cost is >0 there is nothing else to do so it goes
round the loop a second time.

What did you expect it to do?


HTH
-- 
Alan G
Author of the Learn to Program web site
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