problem with postgres

DATABASES = {
    'default': {
       'ENGINE': 'django.db.backends.postgresql',
       'NAME': 'postgres',
        'USER': 'postgres',
        'HOST': 'db',
        'PORT': 5432,
    }
}


db:
    image: postgres:13-alpine
    volumes:
      - postgres_data:/var/lib/postgresql/data/


django.db.utils.OperationalError: could not translate host name "db" to address: Name or service not known