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

That depends on whether you want to start the sequence with F_0  (=0) or
F_1 (=1), I guess.  Given Python's general preferences for zero-based
indexing, I agree that this very serious issue should be fixed.

See

http://www.research.att.com/~njas/sequences/A000045

for an authoritative reference.

The delta (patch) is to change 'b' to 'a' in the while and print
statements and prepend '0 ' to the output line.

tjreedy: The reporter's suggestion seems fine. Prepending a 0 does not
seem to be a good idea.

Senthil: look again. The OP's suggestion *is* to prepend a 0 to the current
1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597
I just specified the delta between current and suggested, should someone
decide to make the change.

That said, def fib2(n), a little further on in 4.6, should get the same
edit as def fib(n) does.

Terry: Oh, sorry. Now I get what you meant by "Prepend O to output
line". That is, Output line from the fib, as part of the patch.  The
changes need to be done at 3 places. Section 3.2, twice in Section 4.6.

Fixed in r76460 through r76463.