Python Particle Stimulation. Any ideas?

'''
    Imagine a "particle" located on the centre square of a two-dimensional
    grid of dimensions 11 by 75.  The particle can only move one square at
    a time, either up, down, left, or right. Associated with each possible
    motion are the following probabilities:

    Up 1/12
    Down 1/12
    Left 1/24
    Right 19/24

    Write a program  that simulates the motion of  the particle within the
    grid,  until it  reaches an  "exit"  at the  square in  row 6,  column
    75. The particle  cannot "penetrate" any of the  four boundaries. Have
    the program repeat  the simulation 10 times and  calculate the average
    total distance travelled by the particle until it exits.
'''

import pprint
import random

# define the rectangle boundary and probability table
ROWS = 11
COLS = 75
EXIT_ROW = 6-1                            # index origin 0
EXIT_COL = 75-1                           # index origin 0
MOVEMENT = (                              # a list of 24 2-tuples
    (( 0, 1),)*2 +  # Up
    (( 0,-1),)*2 +  # Down
    ((-1, 0),)*1 +  # Left
    (( 1, 0),)*19   # Right
    )
#print('MOVEMENT')       # uncomment to display the MOVEMENT list
#pprint.pprint(MOVEMENT) # uncomment to display the MOVEMENT list

# assign the start position at the center
R = ROWS//2  # integer division
C = COLS//2

# prepare the distance traveled
STEPS = 0
BRUISES = 0

while (R != EXIT_ROW) or (C != EXIT_COL):# repeat until finished
    MOVE = MOVEMENT[random.randrange(len(MOVEMENT))] # choose a step and maybe take it
    (COL_STEP,ROW_STEP) = MOVE            # tuple assignment
    PROPOSED_C = C + COL_STEP
    if not (0 <= PROPOSED_C < COLS):      # out-of-bounds
        BRUISES += 1
        continue
    PROPOSED_R = R + ROW_STEP
    if not (0 <= PROPOSED_R < ROWS):
        BRUISES += 1
        continue
    C = PROPOSED_C                        # update position and distance
    R = PROPOSED_R
    STEPS += 1

print('Exit after crashing into the wall %d times and taking %d steps'%(BRUISES,STEPS))

#assertive test
assert 3 == simulation(ROWS = 1, COLS = 4, EXIT_ROW = 0, EXIT_COL = 3, MOVEMENT = ((1,0),), START_ROW = 0, START_COL = 0)

def simulation(
    ROWS = 11,
    COLS = 75,
    EXIT_ROW = 6-1,
    EXIT_COL = 75-1,
    MOVEMENT = ((1,0),),
    START_ROW = 11//2,
    START_COL = 75//2):

    '''drunkard's walk on tilted checkerboard'''
    # fill in the function

NB. dw (<:75 11,:75 6),<.75 11%2[load'j.ijs'
NB. (+/%#)dw"2[10#,:(<:75 11,:75 6),<.75 11%2[load'j.ijs' NB. 10 runs averaged
dw=: 3 : 0
'SHAPE END START'=. y
POSITION=. START
N=. 0
p=. (+/\2r24 2r24 1r24)&(I.?)
while. POSITION -.@:-: END do.
 POSITION=. SHAPE<.0>.POSITION+(p 0){0 _1,0 1,_1,:1
 N=. >:N
end.
)