如何从python中的另一个类访问在类中初始化的数据库？

Question

如何实现MainPage类？你知道吗

import cgi
import os
import logging

from google.appengine.api import users
from google.appengine.ext import webapp
from google.appengine.ext.webapp.util import run_wsgi_app
from google.appengine.ext import db

class Greeting(db.Model):  #setting up database
  a = db.StringProperty(multiline=True)
  b = db.StringProperty(multiline=True)
  c = db.StringProperty(multiline=True)
  d = db.StringProperty(multiline=True)

class MainPage(webapp.RequestHandler):
  def get(self):
##I want to access the content of the database here which is defined in Downloader class. 
##For example let the value of greeting.a be assigned to alpha variable.   


#Entering data to the database
class Downloader(webapp.RequestHandler):
    def get(self):
        greeting=Greeting()
        greeting.a=self.request.GET.get('a')
        greeting.b=self.request.GET.get('b')
        greeting.c=self.request.GET.get('c')
        greeting.d=self.request.GET.get('d')
        greeting.put()

Answer 1

这基本上是通过命名数据库并从另一个类中引用它来解决的

Answer 2

您可以在初始化时将Downloader对象传递到MainPage：

class MainPage(webapp.RequestHandler):
    def __init__(self, downloader):
        self.downloader = downloader

    def get(self):
        self.downloader.get()