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 combinationSum(self, candidates, target):
        candidates.sort()
        self.result = []
        self.dfs(candidates,target,0,[])
        return self.result