'Check to see if some units are valid.
= ERROR CONDITIONS
- If the input units are not in the allowed list, an error is thrown.
= INPUT VARIABLES
- units    The string name of the units to check.'

def checkUnits(self, units):

    if (units not in self.allowed):
        msg = (u"Input    units    '%s'    are    not    one    of    the    supported    types    of    %s" % (units, str(list(six.iterkeys(self.allowed)))))
        raise ValueError(msg)
