flask-Local源碼流程解析

flask中Local源碼數據類型
首先明確：源碼中要構造的數據類型數是這樣的：

__storage__ = {
    用線程或者協程的惟一標識爲鍵: {stack:[ctx(session/request) ,]}
}

其次源碼用Local類構造數據類型，而後又用LocalStack類，做用是操做Local，讓咱們使用起來更方便，

LocalStack類中封裝了push方法，用來給調用Local添加數據，pop方法取數據，


下面來看看具體代碼怎麼實現的

Local類構造數據類型

#用線程或者協程的惟一標識爲鍵,
try:
    # 協程惟一標識
    from greenlet import getcurrent as get_ident
except:
    # 進程惟一標識
    from threading import get_ident

class Local(object):
    # __slots__設置只容許調用的屬性
    __slots__ = ('__storage__', '__ident_func__')

    def __init__(self):
        # __storage__ = {1231:{'stack':[]}}
        object.__setattr__(self, '__storage__', {})     #__storage__={}
        object.__setattr__(self, '__ident_func__', get_ident)  #__ident_func__= get_ident
    #取數據
    def __getattr__(self, name):
        try:
            return self.__storage__[self.__ident_func__()][name]
        except KeyError:
            raise AttributeError(name)
    #主要的數據構造過程
    def __setattr__(self, name, value):
        # name=stack
        # value=[]
        #self對象調用屬性
        ident = self.__ident_func__()  #get_ident()
        storage = self.__storage__     #storage={}
        try:
            storage[ident][name] = value    #storage={get_ident():{stack:[]}}
        except KeyError:
            storage[ident] = {name: value}
    #刪除數據
    def __delattr__(self, name):
        try:
            del self.__storage__[self.__ident_func__()][name]
        except KeyError:
            raise AttributeError(name)

#調用測試
obj = Local()
obj.stack = []
obj.stack.append('胖虎')
obj.stack.append('鹹魚')
print(obj.stack)
print(obj.stack.pop())
print(obj.stack)
"""
數據構造結果：
__storage__ = {
    12312: {stack:[]}
}

"""            

LocalStack類操做Local

# LocalStack 操做Local的類，讓咱們用起來更方法
class LocalStack(object):
    def __init__(self):
        # 以Local對象做爲屬性
        self._local = Local()
    # 向Local放值
    def push(self,value):
        # 會先執行Local類裏面的__setattr__(self, name, value)方法，存儲數據
        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

    #調用local取數據
    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

 

最終實例化LocalStack類爲_request_ctx_stack
經過_request_ctx_stack對象來操做Local，而後把ctx.request / ctx.session放到Local數據類型中

#實例化
_request_ctx_stack = LocalStack()

_request_ctx_stack.push(RequestContext())


def _lookup_req_object(arg):

    ctx = _request_ctx_stack.top()

    return getattr(ctx,arg) # ctx.request / ctx.session

#把request和session都封裝到了Local中
request = functools.partial(_lookup_req_object,'request')
session = functools.partial(_lookup_req_object,'session')