The enemy space ship shoots a rocket towards the player

shoot.py

def enemy_shoots(self):
  nr_of_enemies = len(self.all_enemies)
  if nr_of_enemies > 0:
    enemy_index = random.randint(0, nr_of_enemies - 1)
    start_rocket = None
    for index, enemy in enumerate(self.all_enemies):
      if index == enemy_index:
          start_rocket = enemy.rect.center

    if start_rocket[1] < 400:
      ySpeed = 7
      dx = self.player.rect.centerx - start_rocket[0]
      dy = self.player.rect.centery - start_rocket[1]

      number_of_steps = dy / ySpeed
      xSpeed = dx / number_of_steps

      rocket = Rocket(self.sprites, xSpeed, ySpeed)
      rocket.rect.centerx = start_rocket[0]
      rocket.rect.centery = start_rocket[1]

      self.enemy_rockets.add(rocket)
      self.all_sprites.add(rocket)