Flask--上下文

flask的request和session设置方式比较新颖，如果没有这种方式，那么就只能通过参数的传递。

flask是如何做的呢？

1. 本地线程，保证即使是多个线程，自己的值也是互相隔离。

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#!/usr/bin/env python # -*- coding:utf-8 -*- import threading   local_values = threading.local()     def func(num):     local_values.name = num     import time     time.sleep(1)     print(local_values.name, threading.current_thread().name)     for i in range(20):     th = threading.Thread(target=func, args=(i,), name='线程%s' % i)     th.start()

2. 上下文原理

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#!/usr/bin/env python # -*- coding:utf-8 -*- from functools import partial from flask.globals import LocalStack, LocalProxy   ls = LocalStack()     class RequestContext(object):     def __init__(self, environ):         self.request = environ     def _lookup_req_object(name):     top = ls.top     if top is None:         raise RuntimeError(ls)     return getattr(top, name)     session = LocalProxy(partial(_lookup_req_object, 'request'))   ls.push(RequestContext('c1')) # 当请求进来时，放入 print(session) # 视图函数使用 print(session) # 视图函数使用 ls.pop() # 请求结束pop     ls.push(RequestContext('c2')) print(session)   ls.push(RequestContext('c3')) print(session)

3. Flask内部实现

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#!/usr/bin/env python # -*- coding:utf-8 -*-   from greenlet import getcurrent as get_ident     def release_local(local):     local.__release_local__()     class Local(object):     __slots__ = ('__storage__', '__ident_func__')       def __init__(self):         # self.__storage__ = {}         # self.__ident_func__ = get_ident         object.__setattr__(self, '__storage__', {})         object.__setattr__(self, '__ident_func__', get_ident)       def __release_local__(self):         self.__storage__.pop(self.__ident_func__(), None)       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)     class LocalStack(object):     def __init__(self):         self._local = Local()       def __release_local__(self):         self._local.__release_local__()       def push(self, obj):         """Pushes a new item to the stack"""         rv = getattr(self._local, 'stack', None)         if rv is None:             self._local.stack = rv = []         rv.append(obj)         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:             release_local(self._local)             return stack[-1]         else:             return stack.pop()       @property     def top(self):         """The topmost item on the stack.  If the stack is empty,         `None` is returned.         """         try:             return self._local.stack[-1]         except (AttributeError, IndexError):             return None     stc = LocalStack()   stc.push(123) v = stc.pop()   print(v)