I cant access member from BaseHTTPServer inheritance in python, why?

I wrote a http server program in python, my RequestHandler class inherits from BaseHTTPServer, it initializes the a member, but I cannot access it, where BaseHTTPServer is the first init statement, when I change the order of the init statements it will be correct.

#!/usr/bin/env python

import BaseHTTPServer

class RequestHandler(BaseHTTPServer.BaseHTTPRequestHandler):
    def __init__(self, request, client_address, server):
        BaseHTTPServer.BaseHTTPRequestHandler.__init__(self, request, client_address, server)
        self.a = 0
        print 'aaaa'
    def do_GET(self):
        print self.a  # will cause exception
        self.send_response(200)
        self.send_header('Content-Type', 'text/plain')
        self.end_headers()

server_address = ('127.0.0.1', 8080)
server_class = BaseHTTPServer.HTTPServer
handler_class = RequestHandler
httpd = server_class(server_address, handler_class)
httpd.serve_forever()

      

        
        
        
      

    

when i changed the order __init__

it is correct why?

#!/usr/bin/env python

import BaseHTTPServer

class RequestHandler(BaseHTTPServer.BaseHTTPRequestHandler):
    def __init__(self, request, client_address, server):
        # change init order
        print 'aaaa'
        self.a = 0 
        BaseHTTPServer.BaseHTTPRequestHandler.__init__(self, request, client_address, server)
    def do_GET(self):
        print self.a  # I got
        self.send_response(200)
        self.send_header('Content-Type', 'text/plain')
        self.end_headers()

server_address = ('127.0.0.1', 8080)
server_class = BaseHTTPServer.HTTPServer
handler_class = RequestHandler
httpd = server_class(server_address, handler_class)
httpd.serve_forever()