Python pyparsing 模块，White() 实例源码

def compute(self):

        def getname(obj, name):

            _val = None

            if hasattr(obj, name):
                _val = getattr(obj, name, None)

            if _val is None:
                return _val

            try:
                if _val.isdynamic: #TODO make this work for non-attributes, non-dynamics (use .issingleton? - what about a concat mode?)
                    raise ValueError('Combine plugin cannot process %s because it contains a dynamic class' % name)
            except AttributeError:
                raise TypeError('Expected an attribute but got a %s' % type(_val))

            if _val.issingleton():
                _ret = '%s' % _val[0].raw()
            else:
                _ret = ', '.join(['%s' % v.raw() for v in _val])

            return _ret

        attrmarker = (p.Literal('@') | p.Literal('!'))
        attrmatch = attrmarker.suppress() + p.Word(p.alphanums)

        for i in attrmatch.scanString(self.config):
            x = i[0][0]
            self.__attribs__[x] = getname(self.targetobject, x)

        if all(v is not None for v in self.__attribs__.values()):
            self.computable = True

        if self.computable:

            attrmatch = p.Literal('@').suppress() + p.Word(p.alphanums)
            attrmatch.setParseAction(self.substitute)
            attrlist = p.ZeroOrMore(p.Optional(p.White()) + attrmatch + p.Optional(p.White()))

            self.__result__ = attrlist.transformString(self.config)