Which means property custom_id in discord(pycord) and show examples with this property

I do not understand what is where and why it is needed. I have a cat, but I want to understand what the custom_id is for and, if possible, add the code to the bot.

Documentation

By custom_id I'm assuming you mean the parameter for button creation. See here.

The custom_id is:

The ID of the button that gets received during an interaction. If this button is for a URL, it does not have a custom ID.

Source

Usefulness

Have you ever had the problem of past interactable views not being accessible after a bot restart? Well, the custom_id can be useful for this purpose. If we set the custom_id to anything, after the bot restarts it should keep the view saved (if the bot loads the view & the view has no timeout).

Here's some example code:

import os
import discord
from discord.ui import View, Button

# --- Bot Setup ---
bot = discord.Bot()

@bot.listen()  # ensures that it doesn't override the event method that syncs the bot
async def on_connect():
    bot.add_view(EpicView())  # Add the view to make it persistent
    print("Bot is connected!")


class EpicView(View):  # The persistent view
    def __init__(self, ):
        super().__init__(timeout=None)  # A timeout of None is required

    @discord.ui.button(
        label="Hello!",
        style=discord.ButtonStyle.blurple,
        custom_id="hello_button",
    )
    async def hello(self, button: discord.Button, interaction: discord.Interaction):  # the button that uses the custom_id to make the persistent view
        await interaction.respond("This works!")


@bot.slash_command()
async def send_view(ctx):  # basic slash command to send the view
    view = EpicView()
    await ctx.respond("Hi!", view=view)

This produces:

Above is the first button press

Above is the second button press AFTER the bot restarted.