@classmethod<EOL><INDENT>def lookup_relativedelta_parameter(cls, unit_string):<DEDENT>
try:<EOL><INDENT>return cls._rdp_map()[unit_string.lower()]<EOL><DEDENT>except KeyError:<EOL><INDENT>raise ValueError("<STR_LIT>")<EOL><DEDENT>
>>> lrp = Schedule.lookup_relativedelta_parameter
>>> lrp('Years')
'years'
>>> lrp('yr')
'years'
>>> lrp('s')
'seconds'