config
flask中的配置,都是通过config来控制
那么config究竟是什么?
self.config = self.make_config(instance_relative_config)
再来看make_config函数:
def make_config(self, instance_relative=False):
root_path = self.root_path
if instance_relative:
root_path = self.instance_path
return self.config_class(root_path, self.default_config)
而config_class是什么?
config_class = Config
再转向看config的源码,可以看到Config类继承于字典:
class Config(dict):
也就是说flask的config就是一个特殊的字典,用于保存配置项。
extension
flask是一个微框架,需要使用插件来扩展功能,那么扩展的原理是什么呢?
扩展程序需要与flask交互就需要一种类似wsgi的约定,实现一个扩展主要与两个部分有关:
1.config
2.应用上下文
以广泛应用的flask_sqlalchemy为例,看一下整个过程:
(1)初始化
def __init__(self, app=None, use_native_unicode=True, session_options=None,metadata=None, query_class=BaseQuery, model_class=Model):
...
self.app = app
...
(2)调用init_app
db = SQLAlchemy()
def create_app():
app = Flask(__name__)
db.init_app(app)
return app
(3)init_app执行过程:
1.添加配置项
2.在extension中添加对象
app.extensions['sqlalchemy'] = _SQLAlchemyState(self)
3.添加@app.teardown_appcontext
app.teardown_appcontext是teardown_X() 回调函数用于销毁资源
def init_app(self, app):
if (
'SQLALCHEMY_DATABASE_URI' not in app.config and
'SQLALCHEMY_BINDS' not in app.config
):
warnings.warn(
'Neither SQLALCHEMY_DATABASE_URI nor SQLALCHEMY_BINDS is set. '
'Defaulting SQLALCHEMY_DATABASE_URI to "sqlite:///:memory:".'
)
app.config.setdefault('SQLALCHEMY_DATABASE_URI', 'sqlite:///:memory:')
app.config.setdefault('SQLALCHEMY_BINDS', None)
app.config.setdefault('SQLALCHEMY_NATIVE_UNICODE', None)
app.config.setdefault('SQLALCHEMY_ECHO', False)
app.config.setdefault('SQLALCHEMY_RECORD_QUERIES', None)
app.config.setdefault('SQLALCHEMY_POOL_SIZE', None)
app.config.setdefault('SQLALCHEMY_POOL_TIMEOUT', None)
app.config.setdefault('SQLALCHEMY_POOL_RECYCLE', None)
app.config.setdefault('SQLALCHEMY_MAX_OVERFLOW', None)
app.config.setdefault('SQLALCHEMY_COMMIT_ON_TEARDOWN', False)
track_modifications = app.config.setdefault(
'SQLALCHEMY_TRACK_MODIFICATIONS', None
)
if track_modifications is None:
warnings.warn(FSADeprecationWarning(
'SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and '
'will be disabled by default in the future. Set it to True '
'or False to suppress this warning.'
))
app.extensions['sqlalchemy'] = _SQLAlchemyState(self)
@app.teardown_appcontext
def shutdown_session(response_or_exc):
if app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN']:
if response_or_exc is None:
self.session.commit()
self.session.remove()
return response_or_exc