def METHOD_NAME(self, phase, alias):
    """
    Map an alias to a phase number.
    phase must be >= 0 and alias must be a string
    of characters suitable for python variable names.
    The mapping must be one-to-one.
    """
    assert isinstance(phase,int) and phase >= 0
    assert isinstance(alias,str)
    self.phaseAliasMap[phase] = alias
    self.aliasPhaseMap[alias] = phase