[Python] Game of life in pygame running extremely slow [duplicate]

I am writing a simple version of Conways Game of Life in Python with pygame. It only runs at about 1 fps or even less and I can´t find out why. I´ve read similar questions and found out that nested loops and things like updating the screen to often can cause this but I don´t know how I could change my code. I What is making this code so slow?

The draw_cells function in the main File must be the cause, because its the only one thats called every game tick.

There may be a few unnecessary variables but I don´t think they make a difference.

I am just a beginner, sorry if I am overlooking something completely obvious.

Main File:

import pygame
import sys
import random
from life_cell import LifeCell

class GameOfLife:
"""a class to manage the game mechanics"""
def __init__(self):
pygame.init()
pygame.display.set_caption("Conways Game of life")
self.clock=pygame.time.Clock()

self.screen=pygame.display.set_mode((0,0), pygame.FULLSCREEN)
self.screen_rect=self.screen.get_rect()

self.width=self.screen.get_width()
self.height=self.screen.get_height()
self.hu=self.height/1000
self.wu=self.width/1000
self.sim_running=True

self.size_unit=(self.width+self.height)/3000

self.game_active = True

self.screen=pygame.display.set_mode((0,0), pygame.FULLSCREEN)
self.screen_rect=self.screen.get_rect()


self.grid=[]
self.row=[]
self.draw_grid()
self.draw_cells()
#self.draw_cells()


def run_game(self):
"""main loop of the game"""
while True:
self._check_events()
if self.game_active:
self._update_screen()
self.clock.tick(10)

def _check_events(self):
"""tracks key and mouse actions"""
for event in pygame.event.get():
if event.type == pygame.KEYDOWN:
if event.key==pygame.K_SPACE:
pass
elif event.key == pygame.K_s:
self.sim_running=False
#self.guessed_time,self.time_difference=self.Timer.stop_timer(self.time_input)
elif event.key == pygame.K_q:
sys.exit()
if event.type==pygame.MOUSEBUTTONDOWN:
#mouse_pos=pygame.mouse.get_pos()
#self._check_stop_button(mouse_pos)
#self._check_time_selected(mouse_pos)
pass

def draw_grid(self):
self.x_cell_count=self.width/(self.size_unit*10)
self.y_cell_count=self.height/(self.size_unit*10)
print(self.x_cell_count)
print(self.y_cell_count)
self.x_counter=0
self.y_counter=0
while self.y_counter <= self.y_cell_count:
while self.x_counter <= self.x_cell_count:
self.row.append(random.randint(0,1))
self.x_counter=self.x_counter+1
self.x_counter=0
self.grid.append(self.row)
self.y_counter=self.y_counter+1
self.row=[]
self.y_counter=0
self.x_counter=0
print(self.grid)
self.x_cell_count=0
self.y_cell_count=0


def draw_cells(self):

counter=0
grid_lenght=len(self.grid)
self.row=self.grid[0]
row_lenght=len(self.row)
grid=self.grid
X=grid_lenght
Y=row_lenght
while self.y_counter < grid_lenght:
self.row=self.grid[counter]
for cell in self.row:
print(cell,"cell")

i=self.y_counter
j=self.x_counter

total = int((
grid[(j-1)%X] + grid[(j+1)%Y] +
grid[(i-1)%X][j] + grid[(i+1)%X][j] +
grid[(i-1)%X][(j-1)%Y] + grid[(i-1)%X][(j+1)%Y] +
grid[(i+1)%X][(j-1)%Y] + grid[(i+1)%X][(j+1)%Y]))


if total <2 or total>3:
if grid[self.y_counter][self.x_counter]==1:
self.cell=LifeCell(self,self.size_unit*100*self.x_counter,self.size_unit*100*self.y_counter,0)
self.cell.draw_cell()
grid[self.y_counter][self.x_counter]=0
elif self.grid[self.y_counter][self.x_counter]==0 and total ==3:
grid[self.y_counter][self.x_counter]=1
self.cell=LifeCell(self,self.size_unit*100*self.x_counter,self.size_unit*100*self.y_counter,1)
self.cell.draw_cell()

self.x_counter=self.x_counter+1
self.x_counter=0
self.y_counter=self.y_counter+1
self.y_counter=0


def _update_screen(self):
self.draw_cells()
pygame.display.update()

if __name__=="__main__":
LifeGame=GameOfLife()
LifeGame.run_game()


LifeCell File:

import pygame


class LifeCell:
def __init__(self,LifeGame,x_pos,y_pos,color):
self.screen=LifeGame.screen

if color==1:
self.color=(255,255,255)
else:
self.color=(0,0,0)
self.hu=LifeGame.hu
self.wu=LifeGame.wu
self.size_unit=LifeGame.size_unit
self.width=self.size_unit*100
self.height=self.size_unit*100
#self.color=(255,255,255)

self.rect=pygame.Rect(x_pos,y_pos,self.width, self.height)
#self.rect.right=self.screen_rect.right

def draw_cell(self):
self.screen.fill(self.color,self.rect)

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