The snake game

Adjacent blocks in the grid merge when you navigate with the four arrow keys on the keyboard.

def setup():
    size(700, 700)
    background(255)
    global x, y, a, b, selectedRow, selectedColumn, path
    x, y, a, b = (20, 20, 50, 75)
    selectedRow, selectedColumn = (0, 0)
    path = [(0,0)]
    
def draw():
    background(255)
    noStroke()
    
    for row in xrange(0,9):
        for column in xrange(0,9):
            fill(1)
            rect(b*column+x, b*row+y, a, a)
    
    #highlight selected cell
    fill(0)
    rect(b*selectedColumn+x, b*selectedRow+y, a, a)
#create a shape (polyline) by iterating through (x,y) vertexes in our list called "path"
    s = createShape() 
    s.beginShape() 
    s.stroke(0)
    s.noFill()
    s.strokeCap(PROJECT) 
    s.strokeWeight(a) 
    
    for block in path:
        # rect(b*block[0]+x, b*block[1]+y, a, a)
        s.vertex(b*block[0]+x+a/2, b*block[1]+y+a/2)
        
    s.endShape()
    shape(s, 0, 0)
#track which arrow keys are pressed then adds that (x,y) to our list called "path"    
def keyPressed():
    global x, y, a, b, selectedRow, selectedColumn, path
    
    if keyCode == LEFT:
        selectedColumn -= 1
        path.append((selectedColumn,selectedRow))
        
    if keyCode == RIGHT:
        selectedColumn += 1
        path.append((selectedColumn,selectedRow))
        
    if keyCode == UP:
        selectedRow -= 1
        path.append((selectedColumn,selectedRow))
        
    if keyCode == DOWN:
        selectedRow += 1
        path.append((selectedColumn,selectedRow))