> For the complete documentation index, see [llms.txt](https://aiopsclub.gitbook.io/flask-analysis/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://aiopsclub.gitbook.io/flask-analysis/overview-1/flask_configsystem.md). # flask特性之配置系统 我们在使用flask的时候，可以通过`app.config`来去取或者更新flask的配置，此外，flask的作者还针对配置的加载在Config类中提供多种方法，例如：`from_envvar`、`from_pyfile`、`from_object`等多种形式，那么其背后到底是如何实现的呢？今天我们就来看看flask的配置的神秘面纱。\ 源码奉上： ```python from .config import Config from .config import ConfigAttribute class Flask(_PackageBoundObject): config_class = Config # 以下的配置可由Flask的实例对象直接访问与修改，此处的精妙之处就是通过ConfigAttribute描述符类实现的 testing = ConfigAttribute("TESTING") secret_key = ConfigAttribute("SECRET_KEY") session_cookie_name = ConfigAttribute("SESSION_COOKIE_NAME") permanent_session_lifetime = ConfigAttribute( "PERMANENT_SESSION_LIFETIME", get_converter=_make_timedelta ) send_file_max_age_default = ConfigAttribute( "SEND_FILE_MAX_AGE_DEFAULT", get_converter=_make_timedelta ) use_x_sendfile = ConfigAttribute("USE_X_SENDFILE") default_config = ImmutableDict( { "ENV": None, "DEBUG": None, "TESTING": False, "PROPAGATE_EXCEPTIONS": None, "PRESERVE_CONTEXT_ON_EXCEPTION": None, "SECRET_KEY": None, "PERMANENT_SESSION_LIFETIME": timedelta(days=31), "USE_X_SENDFILE": False, "SERVER_NAME": None, "APPLICATION_ROOT": "/", "SESSION_COOKIE_NAME": "session", "SESSION_COOKIE_DOMAIN": None, "SESSION_COOKIE_PATH": None, "SESSION_COOKIE_HTTPONLY": True, "SESSION_COOKIE_SECURE": False, "SESSION_COOKIE_SAMESITE": None, "SESSION_REFRESH_EACH_REQUEST": True, "MAX_CONTENT_LENGTH": None, "SEND_FILE_MAX_AGE_DEFAULT": timedelta(hours=12), "TRAP_BAD_REQUEST_ERRORS": None, "TRAP_HTTP_EXCEPTIONS": False, "EXPLAIN_TEMPLATE_LOADING": False, "PREFERRED_URL_SCHEME": "http", "JSON_AS_ASCII": True, "JSON_SORT_KEYS": True, "JSONIFY_PRETTYPRINT_REGULAR": False, "JSONIFY_MIMETYPE": "application/json", "TEMPLATES_AUTO_RELOAD": None, "MAX_COOKIE_SIZE": 4093, } ) def __init__( self, import_name, static_url_path=None, static_folder="static", static_host=None, host_matching=False, subdomain_matching=False, template_folder="templates", instance_path=None, instance_relative_config=False, root_path=None, ): # 省略其他逻辑 保留配置相关的代码 # 初始化配置cofnig self.config = self.make_config(instance_relative_config) def make_config(self, instance_relative=False): root_path = self.root_path if instance_relative: root_path = self.instance_path defaults = dict(self.default_config) defaults["ENV"] = get_env() defaults["DEBUG"] = get_debug_flag() return self.config_class(root_path, defaults) ``` 由代码可知，Flask类在初始化时就进行配置的初始化，即`self.config = self.make_config(instance_relative_config)`，此处调用`make_config`方法，返回`self.config_class`所对应的类Config的实例化对象，在Config的实例化的时候，将默认配置`self.default_config`一起加载，并最终将生产的Config实例化对象赋予`self.config`，到此flask的配置的加载逻辑就结束，在开发时，直接可以操作`app.config`来进行读取和修改。\ 在代码中可以看到，flask通过描述符类ConfigAttribute将某些配置直接绑定在Flask类上，这样我们就可以直接修改Flask类实例对象的属性来达到修改配置的目的，比如`app.testting=True`，此处值得我们来学习，描述符类虽然比较抽象，但威力很大，后续将专门说说python的描述符类。 接下来看一下Config类的实现： ```python class Config(dict): def __init__(self, root_path, defaults=None): dict.__init__(self, defaults or {}) self.root_path = root_path def from_envvar(self, variable_name, silent=False): if not rv: if silent: return False raise RuntimeError( "The environment variable %r is not set " "and as such configuration could not be " "loaded. Set this variable and make it " "point to a configuration file" % variable_name ) return self.from_pyfile(rv, silent=silent) def from_pyfile(self, filename, silent=False): filename = os.path.join(self.root_path, filename) d = types.ModuleType("config") d.__file__ = filename try: with open(filename, mode="rb") as config_file: exec(compile(config_file.read(), filename, "exec"), d.__dict__) except IOError as e: if silent and e.errno in (errno.ENOENT, errno.EISDIR, errno.ENOTDIR): return False e.strerror = "Unable to load configuration file (%s)" % e.strerror raise self.from_object(d) return True def from_object(self, obj): if isinstance(obj, string_types): obj = import_string(obj) for key in dir(obj): if key.isupper(): self[key] = getattr(obj, key) def from_json(self, filename, silent=False): filename = os.path.join(self.root_path, filename) try: with open(filename) as json_file: obj = json.loads(json_file.read()) except IOError as e: if silent and e.errno in (errno.ENOENT, errno.EISDIR): return False e.strerror = "Unable to load configuration file (%s)" % e.strerror raise return self.from_mapping(obj) def from_mapping(self, *mapping, **kwargs): mappings = [] if len(mapping) == 1: if hasattr(mapping[0], "items"): mappings.append(mapping[0].items()) else: mappings.append(mapping[0]) elif len(mapping) > 1: raise TypeError( "expected at most 1 positional argument, got %d" % len(mapping) ) mappings.append(kwargs.items()) for mapping in mappings: for (key, value) in mapping: if key.isupper(): self[key] = value return True def get_namespace(self, namespace, lowercase=True, trim_namespace=True): rv = {} for k, v in iteritems(self): if not k.startswith(namespace): continue if trim_namespace: key = k[len(namespace) :] else: key = k if lowercase: key = key.lower() rv[key] = v return rv def __repr__(self): return "<%s %s>" % (self.__class__.__name__, dict.__repr__(self)) ``` 从Config的源码中可以看到， Config类本质上是dict的子类，所以dict的原生的各种方法，Config同样支持。另外Config类中定义了多种加载配置的方法，包括`from_envvar`、`from_pyfile`、`from_object`、`from_json`、`from_mapping`、`get_namespace`。 from\_开头的方法实现起来简单，我们可以根据自己的需求来选择使用何种加载配置的方法。在此，我们说说`get_namespace`方法，由实现可知，改方法是匹配所有以参数namespace开头的配置项，让我们看一个例子： ```python app.config['IMAGE_STORE_TYPE'] = 'fs' app.config['IMAGE_STORE_PATH'] = '/var/app/images' app.config['IMAGE_STORE_BASE_URL'] = 'http://img.website.com' image_store_config = app.config.get_namespace('IMAGE_STORE_') `image_store_config`: { 'type': 'fs', 'path': '/var/app/images', 'base_url': 'http://img.website.com' } ``` 通过`get_namespace`方法，可以方便的寻找同一类配置。 配置的相关操作：\ 修改： * app.config\["example"] = "example" * app.testting = False 这种方式默认只提供有限的配置项 * app.config.update(TESTING=True) 删除： * del app.config\["example"] 参考文档： * [flask config文档](https://flask.palletsprojects.com/en/1.1.x/config/#configuration-basics) --- # Agent Instructions This documentation is published with GitBook. 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