I have 2 python versions installed under my mac osx sierra: python 3.5 python 2.7
I installed pyinstaller under python3.5 with this command:
python3
None of the solutions have worked for me so i tried to uninstall pyinstaller via the command
py -m pip uninstall pyinstaller
The last path they gave was a path to the script "pyinstaller.exe". So all I did was drag and drop and it worked!