Docker and psycopg2: Cannot assign requested address to server at "localhost"

I try to connect to a database using python library psycopg2. Here is the library I use: https://github.com/brunolnetto/psycopg-operational-error. The steps to reproduce are:

Install dependencies: pip install -r requirements.txt;
Host the database: docker compose up -d
Run script: python3 main.py

docker-compose.yml

version: '3.9'

services:
  postgres:
    image: postgres:latest
    restart: always
    env_file: .env
    ports:
      - "5432:5432"
    volumes:
      - postgres_data:/var/lib/postgresql/data

volumes:
  postgres_data:

main.py

from psycopg2 import connect

from os import getenv

DB_USER = getenv('POSTGRES_USER')
DB_PASS = getenv('POSTGRES_PASSWORD')
DB_HOST = getenv('POSTGRES_HOST', 'localhost')
DB_PORT = getenv('POSTGRES_PORT', '5432')
DB_NAME = getenv('POSTGRES_NAME')

try:
    conn = connect(
        database=DB_NAME,
        user=DB_USER,
        password=DB_PASS,
        host=DB_HOST,
        port=DB_PORT
    )
    print("Database connected successfully")
except Exception as e:
    print(f"Database not connected successfully: {e}")

docker-library / docker

Docker and psycopg2: Cannot assign requested address to server at "localhost" #494