Question

here is my code:

class longInputException(Exception):
    def __init__(self, length, max):
        Exception.__init__(self)
        self.length = len(length)
        self.max = max

try:
    max = 3
    s = raw_input('Enter something-->')
    if len(s) > max:
        raise longInputException(s, max)

except longInputException, x:
    print 'longInputException: the input was of length %d, \
was expecting less than or equal to %d' % (x.length, x.max)

else:
    print 'No exception was raised.'

What I don’t understand is why x is used in the longInputException‘s except statement. why not just used self in the substitution tuple?

Answer 1

self is the name of the current object within __init__() method (because you have provided self as the first argument in __init__()‘s definition), it is not accessible outside of it.

Optionally you can do something like that (although this is not something you should do, as this may confuse people about which variable is which):

except longInputException, self:
    print 'longInputException: the input was of length %d, \
was expecting less than or equal to %d' % (self.length, self.max)

else:
    print 'No exception was raised.'

Does it answer your question?

You can learn more about that by reading about closures and namespaces in Python.