stuck with python, please advise

[pwolf]

so im trying to make it so that pressing enter without inputting any value, will break the loop, however, an empty string can be used because of
for i in range(len(x_str_array)):
x[i] = int(x_str_array[i]) bit.

'Exercise 7.3'

# modified program from exercise 7.2

a=1
z=""
while x !=z:
    x_str = raw_input('Enter Start,Stop,Increment: ')
    if x==z:
        break
    else:
        x_str_array = x_str.split(',') # splits the string where a comma pops up
        x = range(len(x_str_array)) # Preallocation step- makes x= the same length as x_str_array
        for i in range(len(x_str_array)):
            x[i] = int(x_str_array[i])
        a=x[0]
        b=x[1]
        c=x[2]
        for number in range(a,b,c):
            print "number:", number, " square:", number**2, " cube:", number**3

please advise me on this.

p.s yes i am a complete novie, haha

i thought maybe using an empty tuple or list or something, but that wouldn't work either.

[Samhain13]

so that pressing enter without inputting any value, will break the loop

while True:
    # Get some user input.
    x_str = raw_input("Someting: ")
    # If the user simply hits enter or supplies a string full of spaces, break.
    if not x_str or x_string.isspace():
        break
    # More stuff here.

Happy new year!