Fluid flow

from tkinter import *

tk=Tk()
WIDTH=4000
HEIGHT=4000
canvas=Canvas(tk,width=WIDTH,height=HEIGHT)
tk.title('conduction')
canvas.pack()

COLUMNS=20
ROWS=20
SIDE=25
ITERATIONS=50
dt=.01

class Particles:
	def __init__(self,x,y,press):
		self.vel=[0,0]
		self.shape=canvas.create_rectangle(SIDE*x,SIDE*y,SIDE*x+SIDE,SIDE*y+SIDE,fill=('#'+2*str(press)+'00'+2*str(9-press)))
		self.line=canvas.create_line(SIDE*x,SIDE*y,SIDE*x+self.vel[0],SIDE*y+self.vel[1],width=5)
		self.press=press
		
	def press_transfer(self,below,right,Source):
		try:
			vert_grad=self.press-below.press
			below.vel[1]+=vert_grad*dt
			self.vel[1]-=vert_grad*dt
			below.press+=below.vel[1]*self.press*dt
			self.press-=below.vel[1]*self.press*dt
		except:
			self.press-=self.vel[1]*self.press*dt
		try:
			hor_grad=self.press-right.press
			right.vel[0]+=hor_grad*dt
			right.press+=right.vel[0]*self.press*dt
			self.press-=right.vel[0]*self.press*dt
		except:
			self.press-=self.vel[0]*self.press*dt
	def color_change(self):
		canvas.itemconfigure(self.shape,fill='#'+2*str(int(self.press))+'00'+2*str(int(9-self.press)))
		canvas.coords(self.line,SIDE*x+SIDE/2,SIDE*y+SIDE/2,SIDE*x+self.vel[0]*20+SIDE/2,SIDE*y+self.vel[1]*20+SIDE/2)
		tk.update()

particles=[]
for x in range (COLUMNS):
	particles.append([])
	for y in range(ROWS):
		if x<10 and y<10:
			press=9
		else:
			press=0
		
		particles[x].append(Particles(x,y,press))


for t in range(ITERATIONS):
	for x in range (COLUMNS):
		for y in range (ROWS):
			try:
				below=particles[x][y+1]
			except:
				below='none'
			try:
				right=particles[x+1][y]
			except:
				right='none'
			particle=particles[x][y]
			if x==0 and y==0 or x==COLUMNS-1 and y==ROWS-1:
				source=True
			particle.press_transfer(below,right,source)
			particle.color_change()

tk.mainloop()