I'm using Buildozer to convert a python file to android APK (using Kivy) and it gets quite far through the process but then errors.
Any ideas what is causing this error at the end?

toolchain.py: error: unrecognized arguments: --sdk 19 Could
  not find hostpython, will not compile to .pyo (this is normal with
  python3)
Command failed: /usr/bin/python -m pythonforandroid.toolchain apk --debug --bootstrap=sdl2 --dist_name KivyTest --name KivyApp --version 0.1 --package doublejgames.com.kivytest --android_api 19 --sdk 19 --minsdk 9 --private /home/kivy/Desktop/.buildozer/android/app --orientation landscape --copy-libs --arch armeabi-v7a --color=always --storage-dir=/home/kivy/Desktop/.buildozer/android/platform/build

This seems to be the main error:

toolchain.py: error: unrecognized arguments: --sdk 19 Could
  not find hostpython, will not compile to .pyo (this is normal with
  python3)

In my buildozer.spec file, I'm using the requirements:

requirements = kivy, python3crystax==3.6 

I also tried just

requirements = kivy, python3crystax

Any help would be appreciated! Thanks.
The error is the 'error: unrecognized arguments: --sdk 19' part, the rest is not important. The problem arises from a regression in python-for-android, as this argument was removed but is still passed by buildozer. I've re-added the argument (with a deprecation warning) and created a PR to stop buildozer calling it anyway. This means that if you clean everything and try again, the error should no longer occur.
Could not find hostpython, will not compile to .pyo (Buildozer python-to-android)