pkg_resources.py 文件源码

def comparison(cls, nodelist):
        if len(nodelist)>4:
            raise SyntaxError("Chained comparison not allowed in environment markers")
        comp = nodelist[2][1]
        cop = comp[1]
        if comp[0] == token.NAME:
            if len(nodelist[2]) == 3:
                if cop == 'not':
                    cop = 'not in'
                else:
                    cop = 'is not'
        try:
            cop = cls.get_op(cop)
        except KeyError:
            raise SyntaxError(repr(cop)+" operator not allowed in environment markers")
        return cop(cls.evaluate(nodelist[1]), cls.evaluate(nodelist[3]))