fib.py

#!/usr/bin/env python
# coding: utf-8
import click
import math
from functools import partial
from itertools import imap
from sys import stdout


def fib(n, as_float=False):
  # Implementation of a closed form solution for the n-th Fibonacci number.
  # Returns the value as an integer if `as_float` is falsy or else as a floating
  # point representation of that integer.
  #
  # Derivation can be found here:
  # http://www.austinrochford.com/posts/2013-11-01-generating-functions-and-fibonacci-numbers.html
  sqrt5 = math.sqrt(5);
  int_f = (lambda x: x) if as_float else int
  return int_f(
      (1.0 / sqrt5) * (
        math.pow((1 + sqrt5) / 2, n) -
        math.pow((1 - sqrt5) / 2, n)))


def fib_seq(n, **fib_kwargs):
  # Return an iterator over the first n numbers in the Fibonacci sequence. Any
  # additional keyword arguments will be passed to the function generating the
  # n-th Fibonacci number, `fib`.
  fib_kwargs = fib_kwargs or {}
  assert not (n % 1) and n >= 0, "n must be an integer greater than 0"
  return imap(partial(fib, **fib_kwargs), xrange(n))


@click.command()
@click.option('-n',
              required=True,
              type=click.INT,
              help='Number of Fibonacci numbers to generate')
@click.option('as_json', '--json', is_flag=True)
@click.option('as_float', '--float/--int', is_flag=True, default=False)
def main(n, as_json, as_float):
  # Print the first n Fibonacci numbers, with various formatting options.
  seq = imap(str, fib_seq(n, as_float=as_float))
  if as_json:
    stdout.write('[%s]' % ','.join(seq))
  else:
    stdout.write(' '.join(seq))
  stdout.write('\n')
  stdout.flush()

if __name__ == '__main__':
  main()