brew升级'python 3.6.5已经安装'但python版本是3.6.4

Question

brew upgrade暗示'python 3.6.5已安装'

$ brew upgrade python
Updated 2 taps (homebrew/core, caskroom/cask).
==> Updated Formulae
aria2              cake               debianutils        grpc               sops               you-get
aws-sdk-cpp        dbxml              fdroidserver       pilosa             xqilla

Error: python 3.6.5 already installed

然而，

$ python --version
Python 3.6.4 :: Anaconda, Inc.
(ll_env)

如何升级在环境中运行的指定python？