staging fails for python app

[pourquoi42]

I am trying to build a python buildpack based application. rock up fails with below message.

It could well be that this is related to my special setup of package repo and vendor folder. But the error message is very unspecific. How to increase verbosity or debug otherwise?

Running Buildpacks...
-------> Buildpack version 1.5.23
-----> Installing python-3.5.3
Downloaded [https://buildpacks.cloudfoundry.org/dependencies/python/python-3.5.3-linux-x64-105f02b2.tgz]
-----> Installing Setuptools (32.1.0)
Downloaded [https://buildpacks.cloudfoundry.org/dependencies/manual-binaries/setuptools/setuptools-32.1.0-44054eaa.tar.gz]
-----> Installing Pip (9.0.1)
Downloaded [https://buildpacks.cloudfoundry.org/dependencies/manual-binaries/pip/pip-9.0.1-35f01da3.tar.gz]
-----> Installing pip-pop (0.1.1)
Downloaded [https://buildpacks.cloudfoundry.org/dependencies/manual-binaries/pip-pop/pip-pop-0.1.1-d410583a.tar.gz]
-----> Installing pipenv (4.0.1)
Downloaded [https://buildpacks.cloudfoundry.org/dependencies/manual-binaries/pipenv/pipenv-4.0.1-148f753f.tar.gz]
     $ pip install -r requirements.txt
 Failed to compile droplet: exit status 1Deleting the CloudRocker container...
Deleted container.
2017/08/10 17:02:59  Staging failed - have you added a buildpack for this type of application?