Eulerproject 2 Fibonacci calculation

I am as new as you can be to Python and trying to learn by following a few guides and doing little projects simultaneously.

I am currently trying to do the 2nd Eulerproject question regarding Fibonacci numbers. It goes as follows:

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

And this was my attempt at solving it

Fib = [1, 2, 3]
answer_list =

x = Fib[-1]
y = Fib[-2]

while x <= 4000000:
z = x + y
Fib.append(z)

for number in Fib:
if number % 2 == 0:
answer_list.append(number)

answer = sum(answer_list)

print(answer)


When I try to use this code I do not get a response. Can anyone, if possible without giving me the actual answer, point me in the right direction on how to improve?

Thanks in advance and kind regards.

x

x = Fib[-1]

while

1 Answer
1

Much simpler and faster way to do the same:

fib = [1, 1] # something to start with
while fib[-1] < 4000000 :
fib.append( fib[-1] + fib[-2] )
print sum( i for i in fib if i&1 == 0 )


outputs:

4613732


If the upper limit is much higher than 4e6, a better approach would be to avoid creating large lists and just use two variables previous and current for the Fibonacchi numbers generation, and one extra variable to keep the sum of the even elements. Something along the lines of:

previous

current

>>> total = 0
>>> current = previous = 1
>>> while current < 4000000 :
... if current & 1 == 0 : total += current
... previous, current = current, previous + current
...
>>> total
4613732


One extra word of the warning, the last number over 4e6 is 5702887 -- an odd number, so I did not care about removing it from the list in the first code sample. But if you want to be extra careful, add fib.pop() before summing the elements.

fib.pop()

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