OverflowError please help

[solartic]

hi all
im trying to create a function that identifies if a number is a Fibonacci numbers base on:
Fibonacci number - Wikipedia, the free encyclopedia
here is what i did

import math

gratio = (1 + math.sqrt(5))/2#golden ratio
lim = 10**999 #math.log(x[, base])

def isFibon(x):#test if number is a Fibonacci numbers
	if (math.log(math.sqrt(5*x),gratio) + 0.5) == x:
		return 1
	else:
		return 0
		
for n in range(20):
	if isFibon(n) == 1:
		print n

and hear id what i got

Traceback (most recent call last):
File "untitled.py", line 15, in <module>
if isFibon(n) == 1:
File "untitled.py", line 9, in isFibon
if (math.log(math.sqrt(5*x),gratio) + 0.5) == x:
OverflowError: math range error

im planning on using another method but im still curious what all this mean
any help will be appreciated

[chili5]

I'm guessing that means that your function generated a number way too big for python to support. Honestly I'm not sure, but I believe that is what that means.

How about a recursive method?

function fib(int n) {
    if (n == 1) return 1;
    return fib(n-1) + fib(n-2);
}

?

[solartic]

that sounds like it, i guess i forgot even python has a limit with how big its values can be.
thanks the recursive method would work but i had already resorted to a simple loop method
Thanks

[chili5]

You're welcome!

[yamman13]

google "how to think like a computer scientist, learning with python". Its a free set of tutorials to python.

it first introduces this problem very early on, then comes back to it much later in the chapter on lists I think.

[solartic]

thanks ill look it up

[PythonPower]

You could use Decimals instead. They can deal with, theoretically, any finite values and by default work to about 18 significant figures. They are slower than floats though...

I can't paste the link to the Python docs on Decimals since I haven't made 10 posts yet, but Googling for "python decimal" should get you close.

[Xav]

decimal — Decimal fixed point and floating point arithmetic &mdash; Python v2.6.1 documentation

[PythonPower]

Yes, the second link was what I had in mind.

[Xav]

I got rid of the first one to avoid confusion.