How to sum numbers from list(s) in python?

Question

Learning python for two days :) and now I attempting to solve Project Euler problem #2 and I need help.

To be more specific, I need know know how to add numbers that were added to a empty list. I tried 'sum' but doesn't seems to work how the tutorial sites suggest. I'm using python 3. Here's my code so far:

a = 0
b = 1
n = a+b
while (n < 20):
   a, b = b, a + b
   n = a+b
   if n%2 == 0:
       mylist = []
       mylist.append(n)
       print(sum(mylist))

this outputs:

2
8

Now how do I add them? Thanks :)

So, you're asking Python to take the sum of a list with one element. What do you actually want to take the sum of? — Greg Hewgill
– Greg Hewgill, Commented Jul 15, 2012 at 3:30
@inspectorG4dget There's no input, it's generating a Fibonacci sequence, see the problem description: projecteuler.net/problem=2 — Levon
– Levon, Commented Jul 15, 2012 at 3:42

Levon · Accepted Answer · 2012-07-15 03:58:03Z

4

You are doing it right (the summing of the list), the main problem is with this statement:

mylist = []

move it before the while loop. Otherwise you are creating an new empy mylist each time through the loop.

Also, you probably want to print the sum of the list probably after you are done with your loop.

I.e.,

...
mylist = []
while (n < 20):
   a, b = b, a + b
   n = a+b
   if n%2 == 0:
       mylist.append(n)

print(sum(mylist))

edited Jul 15, 2012 at 3:58

answered Jul 15, 2012 at 3:29

Levon

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Comments

Ned Batchelder · Accepted Answer · 2012-07-15 03:30:14Z

2

You are creating a new empty list just before you append a number to it, so you'll only ever have a one-element list. Create the empty mylist once before you start.

answered Jul 15, 2012 at 3:30

Ned Batchelder

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Comments

Robert · Accepted Answer · 2012-07-15 05:05:29Z

1

Since it seems that you have the list issue resolved, I would suggest an alternative to using a list.

Try the following solution that uses integer objects instead of lists:

f = 0
n = 1
r = 0

s = 0

while (n < 4000000):
    r = f + n
    f = n
    n = r
    if n % 2 == 0:
        s += n

print(s)

edited Jul 15, 2012 at 5:05

answered Jul 15, 2012 at 4:40

Robert

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Comments

xiaowl · Accepted Answer · 2012-07-15 03:35:31Z

0

Just as @Ned & @Levon pointed out.

a = 0
b = 1
n = a+b
mylist = []
while (n < 20):
   a, b = b, a + b
   n = a+b
   if n%2 == 0:
       mylist.append(n)
print(sum(mylist))

answered Jul 15, 2012 at 3:35

xiaowl

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