Porting of yeast.js to yeast.py

yeast.py

import time

alphabet = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_'
length = 64
map_h = {}
seed = 0
i = 0
prev = None
import math

#
# Return a string representing the specified number.
#
# @param {Number} num The number to convert.
# @returns {String} The string representation of the number.
# @api public
#
def encode(num):
  encoded = ''

  while True:
    encoded = alphabet[num % length] + encoded
    num = math.floor(float(num) / float(length))

    if not (num > 0):
      break

  return encoded

#
# Return the integer value specified by the given string.
#
# @param {String} str The string to convert.
# @returns {Number} The integer value represented by the string.
# @api public
#
def decode(str):
  decoded = 0

  for i in range(len(str)):
    decoded = decoded * length + map_h[str[i]];

  return decoded

#
# Yeast: A tiny growing id generator.
#
# @returns {String} A unique id.
# @api public
#
def yeast():
  global prev, seed
  now = encode(int(time.time() * 1000))
  
  r = str(now) +'.'+ str(encode(seed))
  seed += 1
  return r

#
# Map each character to its index.
#
for i in range(length):
  map_h[alphabet[i]] = i