'Most of the time, ``PYTHONHOME`` is simply
``spec[\'python\'].prefix``. However, if the user is using an
externally installed python, it may be symlinked. For example,
Homebrew installs python in ``/usr/local/Cellar/python/2.7.12_2``
and symlinks it to ``/usr/local``. Users may not know the actual
installation directory and add ``/usr/local`` to their
``packages.yaml`` unknowingly. Query the python executable to
determine exactly where it is installed.'

@property
def home(self):

    prefix = self.get_config_var('prefix')
    return Prefix(prefix)
