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some more python trouble |
iantharan
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Posts: 27
Location: right behind you...
Joined: 14.04.08
Rank: Hacker Level 3 |
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so, ive been trying to solve another problem in python.
im not sure if all you are familiar with the Fibonacci sequence, but basically its generated by adding the previous to numbers
1, 2, 3, 5, 8, ...etc.
so what im trying to do is find the sum of all the even number below four million
the sequence part is working fine,
however for the sum it always prints 0
num=0
a=1
b=2
while num < 4000000:
sum=0
num=a+b
a=num
num=a+b
b=num
if num%2==0:
sum+=num
if a%2==0:
sum+=a
print "the sum of all the even numbers is", sum
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RE: some more python trouble |
tkearn5000
Member
Posts: 32
Location: US
Joined: 13.04.09
Rank: God |
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You're reinitializing sum=0 each time through the loop. Since the last fibonacci number before 4000000 is odd, sum is 0 at the end. You have to initialize sum outside of the loop.
Also, you're using more variables than you need. The code could be a little cleaner like this:
sum=0
a=1
b=1
while b < 4000000:
if b%2==0:
sum+=b
a, b = b, a+b
print "the sum of all the even numbers is", sum
Edited by tkearn5000 on 16-01-10 18:00 |
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RE: some more python trouble |
iantharan
Member
Posts: 27
Location: right behind you...
Joined: 14.04.08
Rank: Hacker Level 3 |
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that was the problem i was having before with a and b, suprised i didnt see that for sum. thanks |
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RE: some more python trouble |
stdio
Member
Posts: 375
Location: omnipresent
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Rank: God |
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You should read this article:
http://20bits.com/articles/introduction-to-dynamic-programming/
I'm sorry, I cant hear you over the sound of how awesome I am! |
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RE: some more python trouble |
wolfmankurd
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Posts: 1519
Location: UK
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Rank: God |
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Whats the the fibonnachi sequence have to do with the sum of all even numbers under 4million?
This is how the fibonnachi sequences should be done in python...
code bank
I can't even work out how your code works, it may be my stupidity but I have a feeling it's just terrible code try and keep it simple.
BY READING MY POST, YOU ACCEPT IT AS IS AND AGREE TO MY DISCLAIMER OF ALL WARRANTIES, EXPRESS OR IMPLIED, AS WELL AS DISCLAIMERS OF ALL LIABILITY, DIRECT, INDIRECT, CONSEQUENTIAL OR INCIDENTAL, THAT MAY ARISE FROM THE USE OF THIS (MIS)INFORMATION.
Edited by wolfmankurd on 17-01-10 21:26 |
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RE: some more python trouble |
tkearn5000
Member
Posts: 32
Location: US
Joined: 13.04.09
Rank: God |
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I'm pretty sure this is a question from Project Euler. Find the sum of all even numbers in the fibonacci sequence below 4000000.
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RE: some more python trouble |
richohealey
Python Ninja
Posts: 1020
Location: #!/usr/local/bin/python
Joined: 01.05.06
Rank: Ninja |
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#!/usr/bin/python
a, b = 0 1
while 1:
print a
a += b
a, b = a, b
if a < 40000: break
NEXT!
ps you can do it with recursion, map() and self referencing lambda's if you want to try to make your own head explode.
EDIT: Saw that it's homework, sample code broken. Simple/easy fix though.
blog.psych0tik.net
Nice one R3l3ntl3ss^^
Edited by richohealey on 18-01-10 03:50 |
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RE: some more python trouble |
ynori7
Future Emperor of Earth
Posts: 1481
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richohealey wrote:
#!/usr/bin/python
a, b = 0 1
while 1:
print a
a += b
a, b = a, b
if a < 40000: break
Your code is pretty wrong. Missing comma in the first line, "a,b=a,b" does nothing, and since 'a' starts out less than 40000 it will break after one iteration.
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RE: some more python trouble |
stdio
Member
Posts: 375
Location: omnipresent
Joined: 06.04.08
Rank: God |
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wolfmankurd wrote:
Whats the the fibonnachi sequence have to do with the sum of all even numbers under 4million?
This is how the fibonnachi sequences should be done in python...
code bank
I can't even work out how your code works, it may be my stupidity but I have a feeling it's just terrible code try and keep it simple.
First the article, I was half drunk and posted that while reading Fibonacci in his post, so it really doesnt apply as much. Yet the sequence he was calculating did involve the Fibonacci sequence.
Ie it wasnt
2+4+6+...+4000000
It was
2+8+34+....
Interms of your next comment.
How can you say that yours is so much better when its almost the exact code? The only difference is that you have to loop 2 extra times. So if you want to get technical the fib2 way IS better then what you have shown.
Here I took yours from the code bank and made one minor modification to it so that it doesnt print all numbers only the final one you want, and put it into a function.
#!/usr/bin/python
def fib2(n):
n2, n1 = 0, 1
for i in range(n-2):
n2, n1 = n1, n1 + n2
return n2+n1
def wolfs_fib(n):
a = 0
b = 1
for _ in range(n):
a, b = b, a+b
return a
print wolfs_fib(100)
print fib2(100)
EDIT: GODDAMNIT MISINTERPRETATION
I'm sorry, I cant hear you over the sound of how awesome I am!
Edited by stdio on 18-01-10 13:18 |
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RE: some more python trouble |
tkearn5000
Member
Posts: 32
Location: US
Joined: 13.04.09
Rank: God |
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Actually that article is very helpful. I've seen it before, and learned a few new things with a second reading. Solving the above question (Find the sum of all even fibonacci numbers below 4000000) involves a few slight modifications to the code in the article, but the underlying algorithm for calculating fibonacci numbers is still there. For example, rather than calculating n fibonacci numbers, my code calculate all of the fibonacci numbers less than 4000000. At each step, I check to see if the new number I have found is even, if so I increment the sum, then I calculate the next fibonacci number in the same way the article does.
The OP could learn a lot from that article as well, since his code had numerous errors not only in the way he was summing the even numbers, but in the way he was attempting to calculate the fibonacci sequence.
Edited by tkearn5000 on 18-01-10 12:20 |
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| Author |
RE: some more python trouble |
wolfmankurd
Member
Posts: 1519
Location: UK
Joined: 30.05.05
Rank: God |
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stdio wrote:
How can you say that yours is so much better when its almost the exact code? The only difference is that you have to loop 2 extra times. So if you want to get technical the fib2 way IS better then what you have shown.
Here I took yours from the code bank and made one minor modification to it so that it doesnt print all numbers only the final one you want, and put it into a function.
I don't understand your criticism, the code is idiomatic.
Ah lol! I see, you think I read the article you coded, and said it was bad code?
I didn't read the article you posted and I thought it was fairly obvious my comment was directed at OP, This is OP's thread after all.
edit: also, if forced to compare the two code snippets I still reckon mine edges ahead. First single line assignments I think I no nos. And the use of _ especially for throw away variables is better than a named one even if it's only i. But thats just anal nit picking.
BY READING MY POST, YOU ACCEPT IT AS IS AND AGREE TO MY DISCLAIMER OF ALL WARRANTIES, EXPRESS OR IMPLIED, AS WELL AS DISCLAIMERS OF ALL LIABILITY, DIRECT, INDIRECT, CONSEQUENTIAL OR INCIDENTAL, THAT MAY ARISE FROM THE USE OF THIS (MIS)INFORMATION.
Edited by wolfmankurd on 18-01-10 16:34 |
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RE: some more python trouble |
stdio
Member
Posts: 375
Location: omnipresent
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Rank: God |
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AHHHH edited.
I'm sorry, I cant hear you over the sound of how awesome I am!
Edited by stdio on 18-01-10 13:16 |
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