def interval(start, stop =None, step = 1 ):
    'Imitates range() for step >0 '
    if stop is None:
        start, stop = 0, start #since start is already 0, why isn't stop as well?
        print start,stop , step
    result = []
    i = start
    while i< stop:
        result.append(i)
        i+=step
    return result

start, stop = 0, start

start = 0
stop = start

a = 1
a, b = 0, a

import dis
dis.dis(compile("a = 1; a, b = 0, a", "<string>", "exec"))

6 LOAD_CONST               1 (0)
              9 LOAD_NAME                0 (a)

13 STORE_NAME               0 (a)
             16 STORE_NAME               1 (b)