Python pyparsing 模块，Empty() 实例源码

def _create_simple_statements():
    global binary, ident, rvalue, simple_statement, semi, comp, number, slot_id, callrpc_stmt, generic_statement, streamer_stmt, stream, selector

    if simple_statement is not None:
        return

    meta_stmt = Group(Literal('meta').suppress() + ident + Literal('=').suppress() + rvalue + semi).setResultsName('meta_statement')
    require_stmt = Group(Literal('require').suppress() + ident + comp + rvalue + semi).setResultsName('require_statement')
    set_stmt = Group(Literal('set').suppress() - (ident | number) - Literal("to").suppress() - (rvalue | binary) - Optional(Literal('as').suppress() + config_type) + semi).setResultsName('set_statement')
    callrpc_stmt = Group(Literal("call").suppress() + (ident | number) + Literal("on").suppress() + slot_id + Optional(Literal("=>").suppress() + stream('explicit_stream')) + semi).setResultsName('call_statement')
    streamer_stmt = Group(Optional(Literal("manual")('manual')) + Optional(oneOf(u'encrypted signed')('security')) + Optional(Literal(u'realtime')('realtime')) + Literal('streamer').suppress() -
                          Literal('on').suppress() - selector('selector') - Optional(Literal('to').suppress() - slot_id('explicit_tile')) - Optional(Literal('with').suppress() - Literal('streamer').suppress() - number('with_other')) - semi).setResultsName('streamer_statement')
    copy_stmt = Group(Literal("copy").suppress() - Optional(oneOf("all count average")('modifier')) - Optional(stream('explicit_input') | number('constant_input')) - Literal("=>") - stream("output") - semi).setResultsName('copy_statement')
    trigger_stmt = Group(Literal("trigger") - Literal("streamer") - number('index') - semi).setResultsName('trigger_statement')

    simple_statement = meta_stmt | require_stmt | set_stmt | callrpc_stmt | streamer_stmt | trigger_stmt | copy_stmt

    # In generic statements, keep track of the location where the match started for error handling
    locator = Empty().setParseAction(lambda s, l, t: l)('location')
    generic_statement = Group(locator + Group(ZeroOrMore(Regex(u"[^{};]+")) + Literal(u';'))('match')).setResultsName('unparsed_statement')

def __init__(self, rule):
        self.rule = rule
        self.opener = self.rule['opener']
        self.closer = self.rule['closer']
        self.columns = self.rule.get('columns', -1)

        nested = nestedExpr(opener=self.opener, closer=self.closer,
                            content=CharsNotIn(self.opener + self.closer))
        if self.columns < 0:
            self.nested = OneOrMore(nested)
        else:
            self.nested = nested * self.columns + Or([CharsNotIn('\n'), Empty()])