code: def checkifDownloadExist(self,username,password,download , name):
          
          try:
              request = urllib2.Request(download)
              base64string = base64.encodestring('%s:%s' % (username, password)).replace('\n', '')
              request.add_header("Authorization", "Basic %s" % base64string)   
              result = urllib2.urlopen(request)
              try:
                  f=open(self.zip_dir+'/'+name+'.tgz', 'wb')
                  f.close()
                  return True
              except urllib2.HTTPError:  
                  return False
          except urllib2.HTTPError:  
              return False
docs: Download single image from Landsat on Google Storage
          Arguments:
              row - string in this format xxx, e.g. 003
              path - string in this format xxx, e.g. 003
              name - zip file name without .tar.bz e.g. LT81360082013127LGN01
              sat_type - e.g. L7, L8, ...