Flask 进阶session和上下文管理解析

session的源码流程

将session放置在redis中

安装

pip install flask-session

使用

import redis
from flask import Flask,request,session
from flask.sessions import SecureCookieSessionInterface
from flask_session import Session

app = Flask(__name__)
app.config['SESSION_TYPE'] = 'redis'
app.config['SESSION_REDIS'] = redis.Redis(host='140.143.227.206',port=6379,password='')
Session(app)

@app.route('/login')
def login():
    session['user'] = 'alex'
    return 'asdfasfd'

@app.route('/home')
def index():
    print(session.get('user'))

    return '...'

if __name__ == '__main__':
    app.run()

上下文管理基础

上下文管理之基础threading.local

1.threading.local

• 实例化一个local对象
• obj.xxxx=i会触发__setattr__ 设置值
• obj.xxxx的会触发__getattr__取值
• local能为每一个线程开辟一个新的空间,让每个线程的资源相互不干扰

import threading,time
from threading import local
obj=local()
def task(i):
    obj.xxxxx = i
    time.sleep(2)
    print(obj.xxxxx,i)

for i in range(0,10):
    t=threading.Thread(target=task,args=(i,))
    t.start()

2.用字典替换local

import threading,time
from threading import local

obj=local()
DIC={}
def task(i):
    ident = threading.get_ident()
    if ident in DIC:
        DIC[ident]['xxxx']=i
    else:
        DIC[ident]={'xxxx':i}
    time.sleep(2)
    print(DIC[ident]['xxxx'],i,ident)
for i in range(0,10):
    t=threading.Thread(target=task,args=(i,))
    t.start()

• ident = threading.get_ident() 获取线程的唯一标识

• 将所有的数据根据线程唯一标示为key存放到字典里,那么该方法也可以避免线程资源冲突...因为DIC是一个全部变量字典

3. 重写local支持协程

import threading,time,greenlet
try:
    get_ident=greenlet.getcurrent
except Exception as e:
    get_ident=threading.get_ident
class Local(object):
    DIC={}
    def __getattr__(self, item):
        ident = get_ident()
        print(ident)
        if ident in self.DIC:
            return self.DIC[ident].get(item)
        return None
    def __setattr__(self, key, value):
        ident= get_ident()
        if ident in self.DIC:
            self.DIC[ident][key]=value
        else:
            self.DIC[ident]={key:value}
obj=Local()
def task(i):
    obj.ha=i
    time.sleep(2)
    print(obj.ha)
for i in range(0,10):
    t= threading.Thread(target=task,args=(i,))
    t.start()

上下文管进阶理解

1.偏函数

# by luffycity.com
import functools
def index(a1,a2):
    return a1 + a2
# 原来的调用方式
# ret = index(1,23)
# print(ret)
# 偏函数，帮助开发者自动传递参数
new_func = functools.partial(index,666)
ret = new_func(1)
print(ret)

2.执行父类方法

class Base(object):
    def func(self):
        print('Base.func')
class Foo(Base):
    def func(self):
        # 方式一：根据mro的顺序执行方法
        # super(Foo,self).func()
        # 方式二：主动执行Base类的方法
        # Base.func(self)

        print('Foo.func')
obj = Foo()
obj.func()

# print(Foo.__mro__)

3.object.__setattr__

class Foo(object):
    def __init__(self):
        # self.storage = {}
        # 在父类的setattr设置storage为空列表
        object.__setattr__(self,'storage',{})
    def __getattr__(self, item):
        print item

    def __setattr__(self, key, value):
        print(key,value,self.storage)

obj = Foo()
obj.xx = 123

• obj=Foo() 实例化对象会执行,__new__......再执行__init__方法加上object.__setattr__会执行object类的方法设置值
• obj.xx=123设置值会执行该类的__setattr__

4.Flask  Local源码

• local是用来给每个线程或者协程开辟一个空间

try:
    from greenlet import getcurrent as get_ident
except:
    from threading import get_ident
class Local(object):
    __slots__ = ('__storage__', '__ident_func__')

    def __init__(self):
        # __storage__ = {1231:{'stack':[]}}
        object.__setattr__(self, '__storage__', {})
        object.__setattr__(self, '__ident_func__', get_ident)

    def __getattr__(self, name):
        try:
            return self.__storage__[self.__ident_func__()][name]
        except KeyError:
            raise AttributeError(name)

    def __setattr__(self, name, value):
        ident = self.__ident_func__()
        storage = self.__storage__
        try:
            storage[ident][name] = value
        except KeyError:
            storage[ident] = {name: value}

    def __delattr__(self, name):
        try:
            del self.__storage__[self.__ident_func__()][name]
        except KeyError:
            raise AttributeError(name)

5.LocalStack源码

• localstack 维护local的列表,维护成一个栈

class LocalStack(object):
    def __init__(self):
        self._local = Local()

    def push(self,value):
        rv = getattr(self._local, 'stack', None) # self._local.stack =>local.getattr
        if rv is None:
            self._local.stack = rv = [] #  self._local.stack =>local.setattr
        rv.append(value) # self._local.stack.append(666)
        return rv

    def pop(self):
        """Removes the topmost item from the stack, will return the
        old value or `None` if the stack was already empty.
        """
        stack = getattr(self._local, 'stack', None)
        if stack is None:
            return None
        elif len(stack) == 1:
            return stack[-1]
        else:
            return stack.pop()

    def top(self):
        try:
            return self._local.stack[-1]
        except (AttributeError, IndexError):
            return None

源码入口

app.__call__
app.wsgi_app

上下文管理request简易流程图

上下文管理request,session流程

• -请求到来之后会触发__call__方法,由__call__方法再次调用wsgi__app方法
• -在wsgi_app方法中:
• -首先将请求相关+空session封装到一个RequestContext对象中即:ctx
• -将ctx交给LocalStack对象,再由LocalStack将ctx添加到local中,Local结构:
• __storage__={
• 线/协程的唯一标识:{stack:[ctx,]}
• -根据请求中的cookie中提取铭文sessionid对应的值,对cookie进行加密+反序列化
• ->视图函数
• -把session中的数据再次加密序列化写入到cookie中.
• -将ctx删除
• -结果返回给用户浏览器
• -断开socket连接.

  #LocalStack是全局的 单例模式
  _request_ctx_stack = LocalStack()
  _app_ctx_stack = LocalStack()
  request = LocalProxy(partial(_lookup_req_object, 'request'))
  session = LocalProxy(partial(_lookup_req_object, 'session'))

上下文管理最终流程图