How to gain program control back after handling the exception?

Question

am developing a python application . I have validated customer id from database. Means if the entered custid is present in database, i am raising an exception. In exception class i am printing the message . So far it is printing the message. But i am not sure how to get control back to the statement where i am taking the input. main app

Custid=input("enter custid)
Validate_custid(Custid) 
Print(Custid)

validate_custid module

From connections import cursor
From customExceptions import invalidcustidException
Def validate_custid(custid):
    Cursor.execute("select count(custid) from customer where custid=:custid",{"custid":custid}) 
    For row in cursor: 
        Count=row[0] 
        If Count==0: 
            Raise invalidcustidException

So far its printing the message in exception.now i want my program to take custid as input whenever this exception occurs. The process should iterate until user enters valid custid.

Its running successfully, for better understanding i have written simple code.i have created alll the required classes in other files. — Bhushan Gadekar, Nov 04 '15 at 01:07
But your *"simple code"* isn't valid Python. Give a [mcve] that stands a chance of running! — jonrsharpe, Nov 04 '15 at 01:07
Looks like he just capitalized the first letter of every line. — personjerry, Nov 04 '15 at 01:12
Yup..sorry i am typing through my mobile so forgot to type it in lower case.module is fine.its working.i am only having trouble with getting control back. — Bhushan Gadekar, Nov 04 '15 at 01:15

score 1 · Answer 1 · answered Nov 04 '15 at 01:15

1

You'll want a try except block.

try:
  # portion of code that may throw exception
except invalidcuspidError:
  # stuff you want to do when exception thrown

See https://docs.python.org/2/tutorial/errors.html for more.

answered Nov 04 '15 at 01:15

personjerry

1,045
8
28

Yup. I know that.but in exceltions except clause, i want to call the function again which was throwing exception until it accepts valid input.i.e. if user enters invalid custid,it should throw exception. Print the message, and will call itself until it gets valid input from customer. – Bhushan Gadekar Nov 04 '15 at 01:22
@BhushanGadekar Perhaps this: Wrap the try block in a while loop that checks a flag. At the beginning of the loop set the flag to false. If the exception triggers, set the flag to true. – personjerry Nov 04 '15 at 01:25

score 1 · Answer 2 · answered Nov 04 '15 at 01:16

1

What you are trying to do is called exception handling. I think the Python docs explain this better than me, so here you go: https://docs.python.org/2/tutorial/errors.html#handling-exceptions

answered Nov 04 '15 at 01:16

Martin Hallén

1,492
1
12
27

score 1 · Accepted Answer · answered Nov 04 '15 at 01:35

You should use a try-except block with else statement:

while True:
    custid = input('Input custom Id: ')
    try:
        # Put your code that may be throw an exception here
        validate_custid(custid)
    except InvalidcustidException as err:
        # Handle the exception here
        print(err.strerror)
        continue # start a new loop
    else:
        # The part of code that will execute when no exceptions thrown
        print('Your custom id {} is valid.'.format(custid))
        break # escape the while loop

Take a look at here: https://docs.python.org/3.4/tutorial/errors.html#handling-exceptions

How to gain program control back after handling the exception?

3 Answers3