Use vector2 in pygame. Collide with the window frame and restrict the ball to the rectangular area

A vector defines a direction and an amount. You have to add the vector to the location of the ball. Sadly pygame.Rect stores integral numbers only, so the location of the object has to be stored in a pygame.math.Vector2, too. You need 1 vector for the location of the object and a 2nd one for the direction. Every time when the location changes, then the .rect attribute has to be set by the rounded location.
If the object hits a surface then the Ball is reflected (.reflect()) by the Normal vector to the surface.

Minimal example: repl.it/@Rabbid76/PyGame-BallBounceOffFrame

import pygame
import random

class Ball(pygame.sprite.Sprite):

    def __init__(self, startpos, velocity, startdir):
        super().__init__()
        self.pos = pygame.math.Vector2(startpos)
        self.velocity = velocity
        self.dir = pygame.math.Vector2(startdir).normalize()
        self.image = pygame.image.load("ball.png").convert_alpha()
        self.rect = self.image.get_rect(center = (round(self.pos.x), round(self.pos.y)))

    def reflect(self, NV):
        self.dir = self.dir.reflect(pygame.math.Vector2(NV))

    def update(self):
        self.pos += self.dir * self.velocity
        self.rect.center = round(self.pos.x), round(self.pos.y)
   
pygame.init()
window = pygame.display.set_mode((500, 500))
clock = pygame.time.Clock()

all_groups = pygame.sprite.Group()
start, velocity, direction = (250, 250), 5, (random.random(), random.random())
ball = Ball(start, velocity, direction)
all_groups.add(ball)

run = True
while run:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    all_groups.update()

    if ball.rect.left <= 100:
        ball.reflect((1, 0))
    if ball.rect.right >= 400:
        ball.reflect((-1, 0))
    if ball.rect.top <= 100:
        ball.reflect((0, 1))
    if ball.rect.bottom >= 400:
        ball.reflect((0, -1))

    window.fill(0)
    pygame.draw.rect(window, (255, 0, 0), (100, 100, 300, 300), 1)
    all_groups.draw(window)
    pygame.display.flip()

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Lets assume you have a group of blocks:

block_group = pygame.sprite.Group()

Detect the collision of the ball and the block_group. Once a collision (pygame.sprite.spritecollide()) is detected, reflect the ball on the block:

block_hit = pygame.sprite.spritecollide(ball, block_group, False)
if block_hit:
    bl = block_hit[0].rect.left  - ball.rect.width/4
    br = block_hit[0].rect.right + ball.rect.width/4
    nv = (0, 1) if bl < ball.rect.centerx < br else (1, 0)
    ball.reflect(nv)