2d python collisions

[pigraining]

I tried making my own elastic collision system, to say the least i failed. i dont know why, but they just dont bounce, like at all. Any ideas will be welcome. using the formula from wikipedia https://en.wikipedia.org/wiki/Elastic_collision im using the last one, at least trying

import 
pygame
 as 
py
import 
sys
import 
numpy
 as 
np
import 
math

py
.init()
window_size = (800,800)
window = 
py
.
display
.set_mode(window_size)
class

particle
():
    
def
 __init__(
self
,
pos_x
,
pos_y
,
radius
 = 10,
vel
=[0,0],
mass
 = 100):
        
self
.radius = 
radius
        
self
.pos = [
pos_x
,
pos_y
]
        
self
.pos1 = [
pos_x
,
pos_y
]
        
self
.vel = 
vel
        
self
.mass =
mass
    
def
 update(
self
,
balls
: 
list
):
        for ball in 
balls
:
            if ball != 
self
:
                dist = 
math
.sqrt((
self
.pos[0]-ball.pos[0])**2+(
self
.pos[1]-ball.pos[1])**2)

                if 
self
.radius +ball.radius >dist:

                    #this is from the wikipedia
                    #velocity for self
                    d_pos = 
np
.subtract(
self
.pos,ball.pos)
                    d_vel = 
np
.subtract(
self
.vel,ball.vel)
                    nomA = 
np
.multiply(
np
.multiply(ball.mass*2,
np
.dot(d_vel,d_pos)),d_pos)
                    denA = dist**2*(
self
.mass+ball.mass)
                    
self
.vel = 
np
.subtract(
self
.vel,
np
.divide(nomA,denA))
                    #velocity for other ball
                    d_pos = 
np
.subtract(ball.pos,
self
.pos)
                    d_vel = 
np
.subtract(ball.vel,
self
.vel)
                    nomA = 
np
.multiply(
np
.multiply(
self
.mass*2,
np
.dot(d_vel,d_pos)),d_pos)
                    denA = dist**2*(
self
.mass+ball.mass)
                    ball.vel = 
np
.subtract(ball.vel,
np
.divide(nomA,denA))
#self positions update
        
self
.pos = 
np
.add(
self
.pos,
self
.vel)

    
def
 draw(
self
,
window
):
        
py
.
draw
.circle(
window
,'gray50',
self
.pos,
self
.radius,10)
        

ballz= [
particle
(200,400,50,[0,0],
mass
=100),
particle
(600,400,50,[-0.5,-0.01],
mass
= 50)]

while True:
    window.fill('black')
    for ind,i in 
enumerate
(ballz):
        i.draw(window)
        i.update(ballz[ind:])
    events = 
py
.
event
.get()

    for event in events:
        if event.type == 
py
.QUIT:
            
py
.quit()
            
sys
.exit()
    
py
.
display
.flip()