The example starts off with 1 being printed, while the series is 
expected to begin with 0 and 1.
The example in 4.6 (defining functions) should have been:

def fib(n):
  a, b = 0, 1
  while a < n:
    print a,
    a, b = b, a+b
fib(2000)

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597