Google App Engine，定义一个预处理类

Question

我试图定义一个基本请求处理类，以便Web应用程序页面可以继承一些基本方法和变量，否则需要为应用程序的每个页面重复定义这些方法和变量。类似于 django 预处理器的类似功能。这是我的基类，其他页面从中继承：

class BasePage(webapp.RequestHandler):
    def __init__(self):    
        self.user = users.get_current_user()    
        self.template_values = {
                'user': self.user,       
                'environ': self,   #I don't like the idea of passing the whole environ object to a template

                ##The below three functions cannot be executed during _init_ because of absence of self.request 
                #'openid_providers': self.openid_providers(),  
                #'logout_url': self.get_logout_url(),
                #'request': self.get_request(),
            }           

    ##A sort of similar functionality like render_to_response in django
    def render_template(self, template_name, values = None, *args, **kwargs):
        #PATH is the directory containing the templates
        if values: 
            for value in values:  self.template_values[value] = values[value]
        self.response.out.write(template.render(PATH+template_name, self.template_values, *args, **kwargs))                 

    ##Returns request as the name suggests
    def logout_url(self):
        return users.create_logout_url(self.request.url)

    ##Returns request as the name suggests
    def request(self):
        return request

    ##Returns openid login urls        
    def openid_providers(self):
        #OPENID_POVIDERS  is a list of dictionary 
        for p in OPENID_PROVIDERS:
             p['login_url'] = users.create_login_url(self.request.get('next', '/') , p['name'], p['url'])
        return OPENID_PROVIDERS  

一切工作正常，除了我无法在初始化期间传递一些变量，因为 self.request 不可用。因此，对于解决方法，我所做的是将整个 self 变量作为模板变量传递。

是否有其他方法向模板提供模板变量（request、logout_url 等）？

Answer 1

比 bgporter 更简单的解决方案是在 webapp.RequestHandler 的 initialize 方法中进行常见设置。这是工作中的一个示例，我们想要向请求对象添加一个类似 Django 的 is_ajax 方法：

class BaseHandler(webapp.RequestHandler):
    def initialize(self, request, response):
        super(BaseHandler, self).initialize(request, response)
        # Add a Django-like is_ajax() method to the request object
        request.is_ajax = lambda: \
            request.environ.get('HTTP_X_REQUESTED_WITH') == 'XMLHttpRequest'

调用此方法是为了，呃，在之前使用当前请求和响应对象初始化每个请求处理程序调用适当的 get 或 post （或其他）方法。

Answer 2

我已经通过使用模板方法模式在我的AppEngine代码中解决了这个问题

基本上，基类看起来像：

class MyBasePage(webapp.RequestHandler):
    def __init__(self):
        # common setup/init stuff here, 
        # omitted for this discussion

    def Setup(self):
        # request handling setup code needed in both GET/POST methods, like
        # checking for user login, getting session cookies, etc.
        # omitted for this discussion

    def get(self, *args):
        self.Setup()
        # call the derived class' 'DoGet' method that actually has 
        # the logic inside it
        self.DoGet(*args)

    def post(self, *args):
        self.Setup()
        # call the derived class' 'DoPost' method 
        self.DoPost(*args)

    def DoGet(self, *args):
        ''' derived classes override this method and 
            put all of their GET logic inside. Base class does nothing.'''
        pass

    def DoPost(self, *args):
        ''' derived classes override this method and 
            put all of their POST logic inside. Base class does nothing.'''
        pass

...您的派生类大多只需要担心这些 DoGet() 和 DoPost() 方法的内部内容。