import random

import numpy

np = 4 # no of particles

ns = 100 # no of steps

positions = numpy.zeros(np) # all particles start at x=0

HEAD = 1; TAIL = 2 # constants

for step in range(ns):

for p in range(np):

coin = random.randint(1,2) # flip coin

if coin == HEAD:

positions[p] += 1 # one unit length to the right

elif coin == TAIL:

positions[p] -= 1 # one unit length to the left