Dealing with errors in input

[ichabod801]

could you explain the replace bit to me in a little more detail please showing how it works. ( I am trying to keep both numbers on the same input line). I've done the while true loop before, but I didn't know how to get it to measure both numbers at once without making a separate loop for each one

>>> value = '2, 3'                   # user enters with a comma
>>> value.split()                    # comma is retained by split()
['2,', '3']
>>> [int(v) for v in value.split()]  # comma prevents converting to integer
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: '2,'
>>> value.replace(',', ' ')                            # replace gets rid of the comma
'2  3'
>>> value.replace(',', ' ').split()                    # you can chain it with split, to get the two numbers entered
['2', '3']
>>> [int(v) for v in value.replace(',', ' ').split()]  # now you can convert to integer
[2, 3]

In terms of measuring two numbers at once, it depends on what you are measuring. If you are just checking a range, you can use min and max:

if min(values) < low or max(values) > high:
    print('Please enter numbers in the range {} to {}.'.format(low, high))

If you are checking them with a function that returns True if the number is valid, you can use map and all:

if all(map(check_function, valid)):
    print('All numbers are valid')

Map will pass each number in valid as a parameter to check_function, and return a list of all the return values. All will return true if all the values in a sequence evaluate to True, and False if any of them don't.