class MainPage(webapp2.RequestHandler):
    def get(self):
      build = createDriveService(user)
      searchFile = build.files().get(fileId='FILEID').execute()
      self.response.write(searchFile)

def createDriveService(userEmail):
    API_KEY = 'APIKEY'
    credentials = AppAssertionCredentials(
        scope='https://www.googleapis.com/auth/drive',
        sub=userEmail)
    http = httplib2.Http()
    http = credentials.authorize(http)

    return build('drive', 'v2', http=http, developerKey=API_KEY)

<"File not found: FILEID">

cannot import SignedJwtAsserionCredentials

from google.appengine.api import app_identity
logging.info('service account : ' + app_identity.get_service_account_name())

def createDriveService():

    SCOPE = 'https://www.googleapis.com/auth/drive'
    API_KEY = 'AIzaSyB9UkK4OH5Z_E4v3Qp6bay6QEgGpzou3bc'     # GAE
    credentials = AppAssertionCredentials(scope=SCOPE)
    logging.info('using service account : ' + app_identity.get_service_account_name())
    http = credentials.authorize(httplib2.Http())
    return build('drive', 'v2', http=http, developerKey=API_KEY)