ImportError: No module named bcrypt._bcrypt In GAE

bcrypt is required to use Flask-Bcrypt
ERROR 2016-11-10 09:07:35,749 wsgi.py:263]
Traceback (most recent call last):
File "/home/emu/google-cloud-sdk/platform/google_appengine/google/appengine/runtime/wsgi.py", line 240, in Handle
handler = _config_handle.add_wsgi_middleware(self._LoadHandler())
File "/home/emu/google-cloud-sdk/platform/google_appengine/google/appengine/runtime/wsgi.py", line 299, in _LoadHandler
handler, path, err = LoadObject(self._handler)
File "/home/emu/google-cloud-sdk/platform/google_appengine/google/appengine/runtime/wsgi.py", line 85, in LoadObject
obj = import(path[0])
File "/home/emu/GCP/gcp-bcrypt/main.py", line 5, in
from flask.ext.bcrypt import Bcrypt
File "/home/emu/GCP/gcp-bcrypt/lib/flask/exthook.py", line 81, in load_module
reraise(exc_type, exc_value, tb.tb_next)
File "/home/emu/GCP/gcp-bcrypt/lib/flask_bcrypt.py", line 27, in
raise e
ImportError: No module named bcrypt._bcrypt

I've create a Google App Engine project. And add Flask-Bcrypt in my requirements.txt file. Then install the dependencies in my project lib folder. When I run the project this gives me above error. But my Flask module which is also a 3rd party library works fine.
What's the solution? I'm using Python 2.7

Start with lib/flask_bcrypt.py at line 27 and the Google App Engine dependency installation described in the issue. Reproduce the Python 2.7 deployment and determine why bcrypt._bcrypt is unavailable; done means Flask-Bcrypt imports successfully on GAE without the reported ImportError.