Создание коллизии в Pygame

Нужно, чтобы человечек при соприкосновении с прямоугольником не мог опуститься вниз, но мог упасть скраю.

import pygame
import random

res_shir = 1080
res_vis = 900
pygame.init()

isJump = False
jumpCount = 10

window = pygame.display.set_mode((res_shir, res_vis))
pygame.display.set_caption("Моя первая игра")

player = pygame.image.load("imgonline-com-ua-Resize-NwejEOZb9SDL7E.jpg")
bg = pygame.image.load("imgonline-com-ua-Resize-dTQqF4gM9xPTOI.jpg")

x = 50
y = 850
speed = 5


class Player(pygame.sprite.Sprite):
    def __init__(self):
        super.__init__()
        self.image = pygame.image.load("imgonline-com-ua-Resize-NwejEOZb9SDL7E.jpg")
        self.rect = self.image.get_rect()

        self.change_x = 0
        self.change_y = 0

        self.level = None

    def update(self):
        self.calc_gravity()

        self.rect.x += self.change_x


class Level(object):
    def __init__(self):
        self.platforms = pygame.sprite.Group()
        self.player = player

        self.background = None

    def update(self):
         screen.blit(bg, (0, 0))

         self.platforms.draw(super)


clock = pygame.time.Clock()
run = True
if run == True:
    obj1_rand = random.randint(100, 980), 830
    obj2_rand = random.randint(100, 980), 680
    obj3_rand = random.randint(100, 980), 530
    obj1 = pygame.Surface((150,50))
    obj2 = pygame.Surface((150,50))
    obj3 = pygame.Surface((150,50))

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

    keys = pygame.key.get_pressed()

    if keys[pygame.K_LEFT] and x >= 0:
        x -= speed
    if keys[pygame.K_RIGHT] and x <= res_shir - 100:
        x += speed
    if keys[pygame.K_q]:
        pygame.QUIT()
    if not(isJump):
        if keys[pygame.K_SPACE]:
            isJump = True
    else:
        if jumpCount >= -10:
            if jumpCount < 0:
                y += (jumpCount ** 2) / 2
        else:
            y -= (jumpCount ** 2) / 2
        jumpCount -= 1
    else:
        isJump = False
        jumpCount = 10
window.blit(bg, (0, 0))
window.blit(player, (x, y))
window.blit(obj1, (obj1_rand))
window.blit(obj2, (obj2_rand))
window.blit(obj3, (obj3_rand))

pygame.display.update()