physics engine problem

 I passed the first step but now I'm stuck on the second one when I try to stop the ball at the left wall it doesn't work here is my program

_________________________________________________________________________1 main.py

import ball
import graphics

output_width = 19
ball_position = 1
ball_speed = 5

for time_step in range(100):
    # Show the ball's position at the current time step.
    print(graphics.show_screen(ball_position, output_width))
    ball_position = ball.move(ball_position, ball_speed, output_width)
    ball_speed = ball.maybe_bounce (ball_position, ball_speed, output_width)

2 ball.py

"""Simulates a ball's movement and collision with the edges of a screen."""

def move(position, speed, right_wall):
    """Returns the ball's new position after one time step.
    The ball moves in straight line at the given speed.
    """
    pos_speed = position + speed
    
    if pos_speed > right_wall:
      return right_wall   
    return pos_speed
    left_wall = 0
    if pos_speed < left_wall:
        return left_wall
        
    
def maybe_bounce(position, speed, right_wall):
    """Returns the ball's new speed, which stays the same unless the ball
    bounces off of a wall.
    """
    if position >= right_wall:
        # Reverses direction and loses a bit of speed.
        speed = speed * -0.75

    return speed

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how do I make the ball stop at the left wall