bullet doesn't bounce in pygame

Question

In the "def Update" section.

According to the place where the four blocks,which are tagged, are placed. The bullet just goes past the screen or stays inside the screen blinking (because it changes its x,y to -x,-y all the time)

Bullet doesn't bounce unlike in other programs I've made. I think the problem is in the position of those four blocks. Can you tell me where to fix?

class Bullet(pygame.sprite.Sprite):
    def __init__(self,centerx,centery,c):
        ...

    def update(self):
        a= pygame.time.get_ticks()
        self.b.append(a)

        #point and shoot
        if self.point == 1:
            self.yspeed = -10
            self.xspeed = 0
        if self.point == 2:
            self.yspeed = 10
            self.xspeed = 0
        if self.point == 3:
            self.yspeed = 0
            self.xspeed = -10
        if self.point == 4: 
            self.yspeed = 0
            self.xspeed = 10

        #bounce
        if self.rect.right>=WIDTH or self.rect.left<=0:
            self.xspeed = -self.xspeed
        if self.rect.top<=0 or self.rect.bottom>=HEIGHT:
            self.yspeed = -self.yspeed

        #kill after 5 sec
        if (a-self.b[0])>=5000:
            del self.b[:]
            self.kill()

        #move according to speed
        self.rect.centerx += self.xspeed
        self.rect.centery += self.yspeed

my full code here - for you to try

import pygame
import random
from os import path

WIDTH = 800
HEIGHT = 600
FPS = 60

BLACK = (0,0,0)
WHITE = (255,255,255)
GREEN = (0,255,0)
RED = (255,0,0)
light_BLUE = (0,255,255)

pygame.init()
pygame.mixer.init()
screen= pygame.display.set_mode((WIDTH,HEIGHT))
clock = pygame.time.Clock()

class Player(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.Surface((30,30))
        self.image.fill(GREEN)
        self.rect = self.image.get_rect()
        self.rect.center = (WIDTH/2,HEIGHT/2)
        self.speed = 0
        self.y_speed = 0

    def update(self):
        self.speed = 0
        self.y_speed = 0
        keystate = pygame.key.get_pressed()
        if keystate[pygame.K_LEFT]:
            self.speed = -3
        if keystate[pygame.K_RIGHT]:
            self.speed = 3
        if keystate[pygame.K_UP]:
            self.y_speed = -3
        if keystate[pygame.K_DOWN]:
            self.y_speed = 3
        self.rect.x+=self.speed
        self.rect.y+=self.y_speed

class Gun(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.Surface((10,10))
        self.image.fill(GREEN)
        self.rect = self.image.get_rect()
        self.rect.center = (WIDTH/2,HEIGHT/2)
        self.a = 0
        self.b = 0
        self.c = 0

    def update(self,player_Cposition):
        keystate = pygame.key.get_pressed()
        if keystate[pygame.K_UP]:
            self.a = player_Cposition[0]
            self.b = player_Cposition[1]-2*self.rect.height
            self.c = 1
        if keystate[pygame.K_DOWN]:
            self.a = player_Cposition[0]
            self.b = player_Cposition[1]+2*self.rect.height
            self.c = 2
        if keystate[pygame.K_LEFT]:
            self.a = player_Cposition[0]-2*self.rect.width
            self.b = player_Cposition[1]
            self.c = 3
        if keystate[pygame.K_RIGHT]:
            self.a = player_Cposition[0]+2*self.rect.width
            self.b = player_Cposition[1]
            self.c = 4
        self.rect.center = [self.a,self.b]

    def shoot(self,x,y,c):
        bullet = Bullet(x,y,c)
        all_sprites.add(bullet)

class Bullet(pygame.sprite.Sprite):
    def __init__(self,centerx,centery,c):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.Surface((8,8))
        self.image.fill(light_BLUE)
        self.rect = self.image.get_rect()
        self.rect.center = [centerx,centery]
        self.point = c
        self.xspeed = 0
        self.yspeed = 0
        self.b = []

    def update(self):
        a= pygame.time.get_ticks()
        self.b.append(a)
        #point and shoot
        if self.point == 1:
            self.yspeed = -10
            self.xspeed = 0
        if self.point == 2:
            self.yspeed = 10
            self.xspeed = 0
        if self.point == 3:
            self.yspeed = 0
            self.xspeed = -10
        if self.point == 4: 
            self.yspeed = 0
            self.xspeed = 10

        #bounce
        if self.rect.right>=WIDTH or self.rect.left<=0:
            self.xspeed = -self.xspeed
        if self.rect.top<=0 or self.rect.bottom>=HEIGHT:
            self.yspeed = -self.yspeed

        #kill after 5 sec
        if (a-self.b[0])>=5000:
            del self.b[:]
            self.kill()

        #move according to speed
        self.rect.centerx += self.xspeed
        self.rect.centery += self.yspeed

all_sprites = pygame.sprite.Group()
player = Player()
gun = Gun()
all_sprites.add(player)
gun_sprites = pygame.sprite.Group()
gun_sprites.add(gun)

running = True
while running:
    #event
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_SPACE:
                gun.shoot(gun.a,gun.b,gun.c)
    #update
    all_sprites.update()
    gun_sprites.update(player.rect.center)
    #draw
    screen.fill(BLACK)
    all_sprites.draw(screen)
    gun_sprites.draw(screen)
    pygame.display.update()
    #clock
    clock.tick(FPS)
pygame.quit()

Answer 1

You are changing bullet speed in two places in your Bullet update function, one workaround could be:

# bounce
    if self.rect.right >= WIDTH or self.rect.left <= 0:
        self.xspeed = -self.xspeed
        self.point = 0
    if self.rect.top <= 0 or self.rect.bottom >= HEIGHT:
        self.yspeed = -self.yspeed
        self.point = 0