Flask开发高级：上【下】文管理源码解析

Bertha 。 2023-03-13 13:54 18阅读 0赞

# 回顾 #

在[前一篇][Link 1]中，我们已经知道Flask是通过把用户的请求信息放入到线程栈中进行存储。例如你的线程id是9528，你进来后，生成一个stack，stack存放的就是9528的请求信息。你是9529、9531等依次对应，所有用户的请求信息都是这样存储。

# {9528:{stack :[ctx(request,session)]}} # 存放的是线程id为9528的请求信息

# 开始 #

接着前一篇继续，在push中，我们知道了Flask的上下文存储机制：

def push(self, obj): # obj= ctx = request_context=(request,session)
     
        """Pushes a new item to the stack"""
    # 这个self往上找，self._local = Local=[{},get_ident]
        rv = getattr(self._local, "stack", None)
        if rv is None:
            self._local.stack = rv = [] # {9528:{stack :[]}}
    # _local对象.stack执行__setattr__方法
        rv.append(obj)
    # {9528:{stack :[ctx(request,session)]}}
        return rv

往回翻到`LocalStack`这里：

# context locals
    _request_ctx_stack = LocalStack() # {9528:{stack :[ctx(request,session)]}}
    # _request_ctx_stack 请求上下文栈，实例化LocalStack()，执行__init__方法
    # _request_ctx_stack._local = Local=[{},get_ident]
    #最后变为： [ {9528:{stack :[ctx(request,session)]}},get_ident]

知道了`LocalStack`存储的值是`[ {9528:{stack :[ctx(request,session)]}},get_ident]`这种形式的。再往下看：

_app_ctx_stack = LocalStack()
    current_app = LocalProxy(_find_app)
    request = LocalProxy(partial(_lookup_req_object, "request")) #partial 偏函数
    session = LocalProxy(partial(_lookup_req_object, "session"))
    g = LocalProxy(partial(_lookup_app_object, "g"))

点击进入到`_lookup_req_object`中：

def _lookup_req_object(name): # name = request
        top = _request_ctx_stack.top
    # _request_ctx_stack._local = [ {9528:{stack :[ctx(request,session)]}},get_ident]
    # 在实例内部别忘了("__storage__", "__ident_func__")与上面数组的小标是对应的
        if top is None:
            raise RuntimeError(_request_ctx_err_msg)
        return getattr(top, name)

进入到`top`中：

def top(self): # self._local = [ {9528:{stack :[ctx(request,session)]}},get_ident]
        """The topmost item on the stack. If the stack is empty, `None` is returned. """
        try:
            return self._local.stack[-1]
    # 对象.stack[-1],调用_local对象中的__getattr__方法
        except (AttributeError, IndexError):
            return None

进入到`_local`对象中，找到`__getattr__`方法：

def __getattr__(self, name): # name = stack 
        try:
    # _request_ctx_stack._local = [ {9528:{stack :[ctx(request,session)]}},get_ident]
    # 在实例内部别忘了("__storage__", "__ident_func__")与上面数组的小标是对应的
            return self.__storage__[self.__ident_func__()][name]
    # self.__ident_func__()获取线程id9528，name就是stack 
    # 拿到[ctx(request,session)] ，然后返回
        except KeyError:
            raise AttributeError(name)

回到`top`这里：

def top(self): # self._local = [ {9528:{stack :[ctx(request,session)]}},get_ident]
        """The topmost item on the stack. If the stack is empty, `None` is returned. """
        try:
            return self._local.stack[-1] # 返回 ctx (request,session)
    # 对象.stack[-1],调用_local对象中的__getattr__方法
        except (AttributeError, IndexError):
            return None

再回到`_lookup_req_object`这里：

def _lookup_req_object(name): # name = request
        top = _request_ctx_stack.top # 拿到 ctx (request,session)
    # _request_ctx_stack._local = [ {9528:{stack :[ctx(request,session)]}},get_ident]
    # 在实例内部别忘了("__storage__", "__ident_func__")与上面数组的小标是对应的
        if top is None:
            raise RuntimeError(_request_ctx_err_msg)
        return getattr(top, name) # # name = request

回到`partial` 这里：

_app_ctx_stack = LocalStack()
    current_app = LocalProxy(_find_app)
    request = LocalProxy(partial(_lookup_req_object, "request")) #partial 偏函数
    # 取出request对象
    session = LocalProxy(partial(_lookup_req_object, "session"))
    g = LocalProxy(partial(_lookup_app_object, "g"))

进入到`LocalProxy`中：

def __init__(self, local, name=None): # local = partial >可得> request
        object.__setattr__(self, "_LocalProxy__local", local) # partial >>> request
    # __setattr__为LocalProxy这个类添加一个__local属性
        object.__setattr__(self, "__name__", name)
    # local是partial偏函数，可以被执行，local中没有__release_local__这个属性
        if callable(local) and not hasattr(local, "__release_local__"): # True
            # "local" is a callable that is not an instance of Local or
            # LocalManager: mark it as a wrapped function.
            object.__setattr__(self, "__wrapped__", local) # partial >>> request

完了，到这里就结束了？别着急，还记得在Flask中可以用`request.method`去判断前端传送数据所用的方法吧。`.method`实质是调用了`request`对象的`__getattr__`方法，由前面可知，`request`对象其实就是`LocalProxy`对象，那我们进`LocalProxy`对象去找找`__getattr__`方法：

def __getattr__(self, name): # 例如 .method 则name = method
        if name == "__members__":
            return dir(self._get_current_object())
        return getattr(self._get_current_object(), name) # name = method

进入到`_get_current_object`中：

def _get_current_object(self):
        """Return the current object. This is useful if you want the real object behind the proxy at a time for performance reasons or because you want to pass the object into a different context. """
        if not hasattr(self.__local, "__release_local__"): # True
            return self.__local() # 往上翻发现，返回的就是request对象
        try:
            return getattr(self.__local, self.__name__)
        except AttributeError:
            raise RuntimeError("no object bound to %s" % self.__name__)

回到`__getattr__`这里，一切都明白了：

请求中的所有数据都是通过反射的方式，从request中获取的

# 总结 #

Flask上下文管理全流程解析：  
![在这里插入图片描述][20200514175446934.png]

[Link 1]: https://blog.csdn.net/qq_35289736/article/details/106112256
[20200514175446934.png]: /images/20230312/58e0b9dffe924abd98555c14175914f5.png