[Tutor] Suggestions for while loop

[Richard Lovely]

2009/5/11 David <david at abbottdavid.com>:
> Hi, I am going through Wesley Chun's book and this is Exercise 8-11;
> Write a program to ask the user to input a list of names, format "Last Name"
> "comma" "First Name". Write a function that manages the input so that
> when/if the user types in the names in the wrong format the error is
> corrected, and keep track of the number of errors. When done sort the list.
>
> Questions;
>
> This;
> answers = raw_input('Enter Name: ')
> index = answers.find(',')
>
> Does not seem to be a very good to me, how could I check for a comma between
> two words?

Look up string.split(), see what happens if the comma isn't in the
string you try to split.  You could also try the "in" operator.

>
> And This;
> try:
>    total_names = int(raw_input('Enter Total Number of Names: '))
> except ValueError:
>    print 'You must enter a number!'
>    total_names = int(raw_input('Enter Total Number of Names: '))
>
> Does not handle the second input for exceptions.

while True: # loop forever
    try:
        total_names = int(raw_input('Enter Total Number of Names: '))
    except ValueError:
        print 'You must enter a number!'
    else:
        # execution only gets to here if no exception occurred
        break # exit the loop

You could do the same using a continue statement in the except:
clause, and break outside the entire structure.

total_names = -1 # set an invalid initial value
while not 0 < total_names < 50: # loop while total_names has an invalid value
    try:
        # If this excepts, total_names is not changed.
        total_names = int(raw_input('Enter Total Number of Names: '))
        # if total_names now has a valid value, the loop exits.
    except ValueError:
        print 'You must enter a number!' # loop continues.


-- 
Richard "Roadie Rich" Lovely, part of the JNP|UK Famile
www.theJNP.com