def get_package_url(cls, package, session=None, silent=False):
        response = get("{}/packages/{}".format(cls.bower_base_uri, package))
        return response.json().get("url", None)
def dfs(self,candidates,target,start,reslist):
        length = len(candidates)
        if target == 0: 
            return self.result.append(reslist)