If you see messages like this when you try to use HtoA
Syntax error: Missing parentheses in call to 'print'
AttributeError: '_Environ' object has no attribute 'has_key'
that means the you have the Python 3 version of Houdini installed.
HtoA 5.6.1 and older do not support Python 3 yet, so you need to download and install the Python 2.7 version of Houdini.
You can get the Python 2.7 version of Houdini here: https://www.sidefx.com/download/daily-builds/?production=true