iterative, functional definition of the fibonacci sequence using reduce()

fibonacci_reduce.py

#!/usr/bin/evn python

# An iterative, functional definition of the fibonacci sequence using reduce()

# This is how I originally wrote this.
# map is going to be removed from the builtin namespace. So the newer 
# version below doesn't use them.
#
# Advocates for removing lambda would consider this to be a good example
# of why it should be removed.
#
def fibo(n):
    """Find the nth fibonacci number
    """
    return reduce( lambda (a, b), count: (b, a+b), xrange(n), (0, 1) )[0]

print map( fibo, xrange(20) )


def fibo_switch((a, b), count):
    """Take a tuple representing the current two numbers of interest in the
    fibonacci sequence and produce a new tuple that advances the sequence.

    We make the first number the current last, and the last number the
    sum of the current first and last.
    """
    return (b, a+b)

def fibo(n):
    """Find the nth fibonacci number
    """
    return reduce( fibo_switch, xrange(n), (0, 1) )[0]

# Print a list of the first 20 fibonacci numbers
print [ fibo(n) for n in xrange(20) ]