app = Flask(__name__)
app.config.from_object('yourapplication.Config')

class Config(object):
    DEBUG = True
    TESTING = False
    DB_USER = os.getenv("DB_USER", "db_user")
    DB_PASSWORD = os.getenv("DB_PASSWORD", "db_password")
    DB_HOST = os.getenv("DB_HOST", "localhost")  # 127.0.0.1"
    DB_PORT = os.getenv("DB_PORT", "5555")
    DB_SCHEMA = "my_schema"
    DB_DATABASE_NAME = "my_database"
    SQLALCHEMY_DATABASE_URI = "postgresql://{}:{}@{}:{}/{}".format(
        DB_USER, DB_PASSWORD, DB_HOST, DB_PORT, DB_DATABASE_NAME)
    SQLALCHEMY_TRACK_MODIFICATIONS = False

my_flask_app cmd1 arg1 arg2

DEBUG=true DB_PORT=1234 my_flask_app cmd1 arg1 arg2

class BaseConfig:
    DEBUG = False
    TESTING = False
    SECRET_KEY = os.getenv('SECRET_KEY', 'a default secret key')
    ...

class DevelopmentConfig(BaseConfig):
    DEBUG = True
    ...


class TestingConfig(BaseConfig):
    TESTING = True
    ...


class ProductionConfig(BaseConfig):
    ...

app = Flask(__name__)
app_settings = os.getenv(
    'APP_SETTINGS',
    'app.config.DevelopmentConfig'
)
app.config.from_object(app_settings)

> APP_SETTINGS=app.config.TestingConfig my_flask_app cmd1 arg1 arg2