流程图如下图所示：

调用相关类如下图所示：

相关代码如下：

from flask import Flask, sessionapp = Flask(__name__)
'''
1. 加密会话数据：在 Flask 中，会话数据存储在客户端的 cookie 中。设置 app.secret_key 可以加密会话 cookie，确保数据的安全性。
2. 签名数据：通过设置 app.secret_key，Flask 可以对客户端发送的数据进行签名，用于验证数据的完整性和来源。
'''
app.secret_key = "1111111"@app.route("/index1")
def index():# 调用session的__setitem__方法# 去ctx中获取session（特殊的字典）session["k1"] = 123return "Index"@app.route("/index2")
def index2():# 调用session的__getitem__方法print(session["k1"])return "Index2"if __name__ == "__main__":app.__call__()app.run()

1、flask实例化之后可以执行的__ call __方法

# self为实例化的app对象
def __call__(self, environ: WSGIEnvironment, start_response: StartResponse
) -> cabc.Iterable[bytes]:# 调用wsgi_app方法return self.wsgi_app(environ, start_response)

2、调用wsgi_app方法：

def wsgi_app(self, environ: WSGIEnvironment, start_response: StartResponse
) -> cabc.Iterable[bytes]:# 调用request_context方法，返回ctx对象'''request_context方法中返回一个类对象，RequestContextctx = RequestContext(self, environ)结合下面的流程最终可以得到ctx中有request(environ),session;将两者打包到一块'''ctx = self.request_context(environ)error: BaseException | None = Nonetry:try:'''对session进行赋值if self.session is None:session_interface = self.app.session_interfaceself.session = session_interface.open_session(self.app, self.request)
​if self.session is None:self.session = session_interface.make_null_session(self.app)'''ctx.push()'''执行视图函数'''response = self.full_dispatch_request()except Exception as e:error = eresponse = self.handle_exception(e)except:  # noqa: B001error = sys.exc_info()[1]raisereturn response(environ, start_response)finally:if "werkzeug.debug.preserve_context" in environ:environ["werkzeug.debug.preserve_context"](_cv_app.get())environ["werkzeug.debug.preserve_context"](_cv_request.get())
​if error is not None and self.should_ignore_error(error):error = None
​ctx.pop(error)

2.1、request_context方法源码如下：

def request_context(self, environ: WSGIEnvironment) -> RequestContext:# 返回RequestContext对象 self 表示实例化的Flask对象app，environ表示wsgi环境return RequestContext(self, environ)

2.1.1、RequestContext类中进行的操作：

def __init__(self,app: Flask,environ: WSGIEnvironment,request: Request | None = None,session: SessionMixin | None = None,
) -> None:self.app = app'''判断如果request是空的话，将其赋值为app.request_class(environ)即： request_class: type[Request] = Requestrequest=Request'''if request is None:request = app.request_class(environ)request.json_module = app.jsonself.request: Request = requestself.url_adapter = Nonetry:self.url_adapter = app.create_url_adapter(self.request)except HTTPException as e:self.request.routing_exception = eself.flashes: list[tuple[str, str]] | None = None'''设置session值'''self.session: SessionMixin | None = session
​self._after_request_functions: list[ft.AfterRequestCallable[t.Any]] = []......

2.2、调用push方法，对session进行赋值：

def push(self) -> None:app_ctx = _cv_app.get(None)
​if app_ctx is None or app_ctx.app is not self.app:app_ctx = self.app.app_context()app_ctx.push()else:app_ctx = None
​self._cv_tokens.append((_cv_request.set(self), app_ctx))
​'''对session进行赋值'''if self.session is None:# session_interface: SessionInterface = SecureCookieSessionInterface()session_interface = self.app.session_interface# SecureCookieSessionInterface.open_session(self.app, self.request)self.session = session_interface.open_session(self.app, self.request)
​if self.session is None:self.session = session_interface.make_null_session(self.app)
​if self.url_adapter is not None:self.match_request()

2.2.1、SecureCookieSessionInterface.open_session(self.app, self.request)方法：由此所知，session是一个特殊的字典。

def open_session(self, app: Flask, request: Request) -> SecureCookieSession | None:s = self.get_signing_serializer(app)if s is None:return None'''如果拿不到值就返回session_class()session_class() ：class SecureCookieSession(CallbackDict, SessionMixin)继承class CallbackDict(UpdateDictMixin, dict):CallbackDict继承dict（字典）'''val = request.cookies.get(self.get_cookie_name(app))if not val:return self.session_class()max_age = int(app.permanent_session_lifetime.total_seconds())try:data = s.loads(val, max_age=max_age)return self.session_class(data)except BadSignature:return self.session_class()

初步学习，继续补充完善......