5 Ways of Fibonacci in Python

After learning so much about development in Python, I thought this article would be interesting for readers and to myself…

This is about 5 different ways of calculating Fibonacci numbers in Python

## Example 1: Using looping technique
def fib(n):
 a,b = 1,1
 for i in range(n-1):
  a,b = b,a+b
 return a
print fib(5)

## Example 2: Using recursion
def fibR(n):
 if n==1 or n==2:
  return 1
 return fib(n-1)+fib(n-2)
print fibR(5)

## Example 3: Using generators
a,b = 0,1
def fibI():
 global a,b
 while True:
  a,b = b, a+b
  yield a
f=fibI()
f.next()
f.next()
f.next()
f.next()
print f.next()

## Example 4: Using memoization
def memoize(fn, arg):
 memo = {}
 if arg not in memo:
  memo[arg] = fn(arg)
  return memo[arg]

## fib() as written in example 1.
fibm = memoize(fib,5)
print fibm

## Example 5: Using memoization as decorator
class Memoize:
 def __init__(self, fn):
  self.fn = fn
  self.memo = {}
 def __call__(self, arg):
  if arg not in self.memo:
   self.memo[arg] = self.fn(arg)
   return self.memo[arg]

@Memoize
def fib(n):
 a,b = 1,1
 for i in range(n-1):
  a,b = b,a+b
 return a
print fib(5)

You may ask, all this is okay, but what’s the best way? Wait for another post on performance of these… Its on the way!

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