Question

What will happen when following functions are executed?

def fib():
x,y = 1,1
while True:
yield x
x,y = y, x+y
def odd(seq):
for number in seq:
if number % 2:
yield number
def under Four Million(seq):
for number in seq:
if number > 4000000:
       break
yield number
       print sum(odd(underFourMillion(fib())))

Answer 1

The code as printed will not execute because it has syntax and indentation errors: under Four Million contains spaces, the function should be named underFourMillion, and the if, yield, and print statements need proper indentation.

The corrected Python 3 version is:

def fib():
    x, y = 1, 1
    while True:
        yield x
        x, y = y, x + y


def odd(seq):
    for number in seq:
        if number % 2:
            yield number


def underFourMillion(seq):
    for number in seq:
        if number > 4_000_000:
            break
        yield number


print(sum(odd(underFourMillion(fib()))))

fib() generates Fibonacci numbers indefinitely. underFourMillion() stops when a number exceeds four million, and odd() keeps only odd numbers. The output is:

4613732

The generator is finite in practice because underFourMillion() stops the iteration.