I'm using the Python "units" package (http://pypi.python.org/pypi/units/) and I've run into some trouble when trying to pickle them. I've tried to boil it down to the simplest possible to case to try and figure out what's going on. Here's my simple test: from units import unit, named_unit from units.predefined import define_units from units.compatibility import compatible from units.registry import REGISTRY a = unit('m') a_p = pickle.dumps(a) a_up = pickle.loads(a_p) logging.info(repr(unit('m'))) logging.info(repr(a)) logging.info(repr(a_up)) logging.info(a.is_si()) logging.info(a_up.is_si()) logging.info( compatible(a,a_up) ) logging.info(a(10) + a_up(10)) The output I'm seeing when I run this is: LeafUnit('m', True) LeafUnit('m', True) LeafUnit('m', True) True True False IncompatibleUnitsError I'd understand if pickling units broke them, if it weren't for the fact that repr() is returning identical results for them. What am I missing? This is using v0.04 of the units package, and Google App Engine 1.4 SDK 1