NameError：未定义全局名称

main.py\", line 2289, in get
    buf=zipf.read(2048)
NameError: global name \'zipf\' is not defined

 def addFile(self,zipstream,url,fname):
     # get the contents          
     result = urlfetch.fetch(url)

     # store the contents in a stream
     f=StringIO.StringIO(result.content)
     length = result.headers[\'Content-Length\']
     f.seek(0)

     # write the contents to the zip file
     while True:
       buff = f.read(int(length))
       if buff==\"\":break
       zipstream.writestr(fname,buff)
       return zipstream

 def get(self):   
    self.response.headers[\"Cache-Control\"] = \"public,max-age=%s\" % 86400
    start=datetime.datetime.now()-timedelta(days=20)
    count = int(self.request.get(\'count\')) if not self.request.get(\'count\')==\'\' else 1000        
    from google.appengine.api import memcache
    memcache_key = \"ads\"
    data = memcache.get(memcache_key)
    if data is None:
      a= Ad.all().filter(\"modified >\", start).filter(\"url IN\", [\'www.koolbusiness.com\']).filter(\"published =\", True).order(\"-modified\").fetch(count)
      memcache.set(\"ads\", a)  
    else:
      a = data
    dispatch=\'templates/kml.html\'
    template_values = {\'a\': a , \'request\':self.request,}
    path = os.path.join(os.path.dirname(__file__), dispatch)
    output = template.render(path, template_values)    
    self.response.headers[\'Content-Length\'] = len(output)    
    zipstream=StringIO.StringIO()
    file = zipfile.ZipFile(zipstream,\"w\")
    url = \'http://www.koolbusiness.com/list.kml\'
    # repeat this for every URL that should be added to the zipfile
    file =self.addFile(file,url,\"list.kml\")
    # we have finished with the zip so package it up and write the directory
    file.close()
    zipstream.seek(0)
    # create and return the output stream
    self.response.headers[\'Content-Type\'] =\'application/zip\'
    self.response.headers[\'Content-Disposition\'] = \'attachment; filename=\"list.kmz\"\' 
    while True:
      buf=zipf.read(2048)
      if buf==\"\": break
    self.response.out.write(buf)