on member join cogs code example

Example 1: how to make a cog discord.py

from discord.ext import commands

class Test_Cog(commands.Cog):
	def __init__(self, bot):
      self.bot = bot # defining bot as global var in class
      
	@commands.Cog.listener() # this is a decorator for events/listeners
    async def on_ready(self):
      print('Bot is ready!.')
      
	@commands.command() # this is for making a command
    async def ping(self, ctx):
		await ctx.send(f'Pong! {round(self.bot.latency * 1000)}')
        
def setup(bot): # a extension must have a setup function
	bot.add_cog(Test_Cog(bot)) # adding a cog

Example 2: how to load a all cogs automatically discord.py

# bot file
import os
from discord.ext import commands

bot = commands.Bot(command_prefix='.')
# I am assuming that you have a test.py cog in a cogs folder
bot.load_extension('cogs.test') # this is good but you can make it better

for filename in os.listdir('./cogs'):
  if filename.endswith('.py'):
    bot.load_extension(f'cogs.{filename[:-3]}')
    
  else:
    print(f'Unable to load {filename[:-3]}')
    
bot.run(token)