Find the sum of all odd Fibonacci numbers less than 2 million

Question

Hello I have been trying to do the opposite of project Euler question 2 (which is to sum of all even Fibonacci numbers less than 4,000,000). I am trying to print the sum of all odd Fibonacci numbers less than 2,000,000 however I cannot seem to get the correct answer. This is the code I have so far

fib1 = 1
fib2 = 2
fibholder = 0 #place holder for the new value
Sum = 0
while fibholder<2000000:
    fibholder = fib1 + fib2
    if fibholder%2==1:
        Sum+=fibholder
    fib1 = fib2
    fib2 = fibholder
print(Sum)

Answer 1

You are skipping the first two odd numbers in the sequence and including the first odd value greater than 2,000,000 in your sum because you calculate the next fibonacci number and increment your total before your while loop checks whether or not the value is less than your limit. You could correct your existing approach by initializing your variables to include the beginning of the sequence and by moving your calculation of the next number in the sequence to the end of your while loop.

total = 1
fib1 = 0
fib2 = 1
fibholder = fib1 + fib2
while fibholder < 2000000:
    if fibholder % 2:
        total += fibholder
    fib1 = fib2
    fib2 = fibholder
    fibholder = fib1 + fib2

print(total)
# 2435423

That said, the logic might be easier to follow if you just generate the odd fibonacci numbers and then handle the sum.

def odd_fibonacci(limit):
    a, b = 0, 1    
    while a < limit:
        if a % 2:
            yield a

        a, b = b, a + b

x = sum(n for n in odd_fibonacci(2000000))
print(x)
# 2435423