Werkzeug的Local系列(5) -LocalStack源码与使用

LocalStack源码

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

    def __release_local__(self):
        self._local.__release_local__()

    def _get__ident_func__(self):
        return self._local.__ident_func__

    def _set__ident_func__(self, value):
        object.__setattr__(self._local, "__ident_func__", value)

    __ident_func__ = property(_get__ident_func__, _set__ident_func__)
    del _get__ident_func__, _set__ident_func__

    def __call__(self):
        def _lookup():
            rv = self.top
            if rv is None:
                raise RuntimeError("object unbound")
            return rv

        return LocalProxy(_lookup)

    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

虽然Local是通过key-value管理对象，但是LocalStack引入了类型为list的stack，这样看起来像stack。

      """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

另外__call__的实现，使得每次调用拿的都是最新push的对象。

    def __call__(self):
        def _lookup():
            rv = self.top
            if rv is None:
                raise RuntimeError("object unbound")
            return rv

        return LocalProxy(_lookup)

使用LocalStack

from werkzeug.local import LocalStack

class Request(object):

    def __init__(self):
        self.url = 'baidu.com'

class User(object):
    
    def __init__(self):
        self.owner = 'www'

request = Request()
user = User()

ls = LocalStack()
ls.push(request)

r = ls()
print(r)
ls.push(user)
# 特别注意的是这里是User对象，调用__call__
r = ls()
print(r)

输出结果：

<main.Request object at 0x7f1566d42e10>
<main.User object at 0x7f1566d42da0>

拿到了Request和User对象实例。