Python while loops

Question

I have this code in python 3,to check for errors on input but i need to determine that the input is an integer and if not to print the error message.

can anyone help me to figure out the code in my while loop. Thanks

price = 110;

ttt = 1;

while price < 0 or price > 100:

    price = input('Please enter your marks for Maths:');
    ttt =ttt +1;
    if ttt >= 2:
        print( 'This is an invalid entry, Please enter a number between 0 and 100')

Answer 1

Use the int() function to convert to an integer. This will raise a ValueError when it cannot do the conversion:

try:
    price = int(price)
except ValueError as e:
    print 'invalid entry:', e

Answer 2

You probably want something like this, which will catch both whether the price is a whole number and whether it is between 0 and 100, and break the loop if these conditions are fulfilled.

while True:
    price = raw_input('Please enter your marks for Maths:')
    try:
        price = int(price)
        if price < 0 or price > 100:
            raise ValueError
        break
    except ValueError:
        print "Please enter a whole number from 0 to 100"

print "The mark entered was", price

Or since you have a manageably small number of possible values you could also do something like:

valid_marks = [str(n) for n in range(101)]
price = None
while price is None:
    price = raw_input('Please enter your marks for Maths:')
    if not price in valid_marks:
       price = None
       print "Please enter a whole number from 0 to 100"