The module entropy_path_loader (used only for running from within the
checkout; otherwise not even installed) is made to provide the _entropy
namespace.
(Other ideas instead of this entropy_path_loader change would be to
reorganise files layout; drop support for running from the checkout as
is - and perhaps require virtualenvs; require sourcing a script that
sets PYTHONPATH. However, as implemented, it is not intrusive, and the
good part is that it is quite isolated, not used in normal usage after
installation. Basically, it only does sys.path + provides _entropy
namespace.)
