You can actually remove the try/except, because if the calculation
key-len(self.fibsseq)+1 <= 0 the for loop won't execute. The for loop will
make sure self.fibsseq is long enough to satisify the return
self.febsseq[key] access:
class Fibs(object):
def __init__(self):
self.fibsseq = [0, 1]
def __getitem__(self, key):
for i in xrange(key - len(self.fibsseq) + 1):
self.fibsseq.append(self.fibsseq[-1] + self.fibsseq[-2])
return self.fibsseq[key]
-Mark
"Emil" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
Hey John thank you for your reply. I came up with this code, it is not
elegant( yet) but i would say that it is more efficient :)
class Fibs(object):
def __init__(self):
self.fibsseq = [0,1]
def __getitem__(self, key):
try:
return self.fibsseq[key]
except IndexError:
for i in xrange(key-len(self.fibsseq)+1):
self.fibsseq.append(self.fibsseq[-1] + self.fibsseq[-2])
return self.fibsseq[key]
----------------------------------------
Date: Thu, 3 Jul 2008 12:59:39 +1200
From: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Subject: Re: [Tutor] Fibonacci series(perhaps slightly off topic)
CC: tutor@python.org
On 03/07/2008, Emil wrote:
I have created a class called Fibs which allow you to access a specific
number in the
Fibonacci series(http://en.wikipedia.org/wiki/Fibonacci_number) But it
seems to me that it
is a bit inefficient, any suggestions on how to make it more efficient?
Does this behaviour seem correct to you? --
class Fibs(object):
... def __init__(self):
... self.fibsseq = [0, 1]
... def __getitem__(self, key):
... for i in xrange(key):
... self.fibsseq.append(self.fibsseq[-1] +
self.fibsseq[-2])
... return self.fibsseq[key]
...
f = Fibs()
f[1]
1
f[1]
1
f[1]
1
f.fibsseq
[0, 1, 1, 2, 3]
Maybe if I examine the first Fibonacci number a few hundred times:
ones = [f[1] for i in xrange(500)]
len(f.fibsseq)
505
Hmm, that's a lot of numbers to calculate when we're only looking at
the first element in the sequence..
(by the way: you might want to replace 'print' with 'return' in your
definition of __getitem__)
(by the way 2: if you follow the above code, and then display
f.fibsseq, you may see some nice curves caused by the " " between each
number. Aren't fibonacci numbers wonderful :-) )
--
John.
_______________________________________________
Tutor maillist - Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor
