怎么理解flask的这段代码呢？
有人能解释一下这一行吗？
g = LocalProxy(lambda: _request_ctx_stack.top.g)
Local Flask
from werkzeug import LocalStack, LocalProxy
# context locals
_request_ctx_stack = LocalStack()
current_app = LocalProxy(lambda: _request_ctx_stack.top.app)
request = LocalProxy(lambda: _request_ctx_stack.top.request)
session = LocalProxy(lambda: _request_ctx_stack.top.session)
g = LocalProxy(lambda: _request_ctx_stack.top.g)
代码的代码在这里： http://pastebin.com/U3e1bEi0
Could anyone explain this line？
g = LocalProxy(lambda: _request_ctx_stack.top.g)
code from flask
from werkzeug import LocalStack, LocalProxy
# context locals
_request_ctx_stack = LocalStack()
current_app = LocalProxy(lambda: _request_ctx_stack.top.app)
request = LocalProxy(lambda: _request_ctx_stack.top.request)
session = LocalProxy(lambda: _request_ctx_stack.top.session)
g = LocalProxy(lambda: _request_ctx_stack.top.g)
code of Local is here: http://pastebin.com/U3e1bEi0
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LocalStack 和 LocalProxy 的 Werkzeug 文档 可能会有所帮助，以及对 < a href="http://en.wikipedia.org/wiki/Web_Server_Gateway_Interface" rel="nofollow">WSGI。
看起来正在发生的事情是创建了一个全局（但空）堆栈
_request_ctx_stack。这适用于所有线程。某些 WSGI 样式对象（current_app、request、session和g）设置为使用顶部项目在全局堆栈中。在某一时刻，一个或多个 WSGI 应用程序被推送到全局堆栈上。然后，例如，当在运行时使用
current_app时，将使用当前的顶级应用程序。如果堆栈从未初始化，则 top 将返回 None，并且您将收到类似 AttributeError: 'NoneType' object has no attribute 'app' 的异常。The Werkzeug documentation for LocalStack and LocalProxy might help, as well as some basic understanding of WSGI.
It appears what is going on is that a global (but empty) stack
_request_ctx_stackis created. This is available to all threads. Some WSGI-style objects (current_app,request,session, andg) are set to use the top item in the global stack.At some point, one or more WSGI applications are pushed onto the global stack. Then, when, for example,
current_appis used at runtime, the current top application is used. If the stack is never initialized, then top will return None and you'll get an exception likeAttributeError: 'NoneType' object has no attribute 'app'.