Random walk's weird outcome in python 3?

Question

I just start learning python and have a problem to print a new location of random walk in 3 dimensions. There is no error popping up, but it\'s obvious that the output (x, y

Answer 1

You set n to a new random number in every if test:

if n < 1/6:
    x = x + 1           # move east
    n = random.random() # generate a new random number

This means the next if test can then also match on the new n, giving you more than one change per step.

Move the n = random.random() step to the top of the loop, generating it only once per step. You probably want to use elif as well to avoid making too many tests:

N = 30  # number of steps

x = 0
y = 0
z = 0

for count in range(N):
    n = random.random() # generate a new random number
    if n < 1/6:
        x = x + 1           # move east
    elif n < 2/6:
        y = y + 1           # move north
    elif n < 3/6:
        z = z + 1           # move up
    elif n < 4/6:
        x = x - 1           # move west
    elif n < 5/6:
        y = y - 1           # move south
    else:
        z = z - 1           # move down

    print("(%d,%d,%d)" % (x,y,z)) 

I also switched to using a for loop over range() so you don't have to manually increment and test count.

This can be further simplified by using a list to store the directions, random.range() to pick an index in that list at random, and random.choice() to pick what direction to change the step in:

N = 30  # number of steps

pos = [0, 0, 0]

for count in range(N):
    index = random.randrange(3) # generate a new random index
    change = random.choice([-1, 1])
    pos[index] += change

    print(tuple(pos))