pyenv suddenly doesn't work after a brew cleanup

I have just run a brew cleanup command to release some of my hard drive space. But after that, I suddenly found my python doesn’t work:

pyenv /usr/local/var/pyenv/shims/python: line 21: /usr/local/Cellar/pyenv/20160310/libexec/pyenv: No such file or directory

As it says, the directory of /usr/local/Cellar/pyenv/20160310/ really does not exist. And the solution can be found from brew info pyenv:

To use Homebrew's directories rather than ~/.pyenv add to your profile:
  export PYENV_ROOT=/usr/local/var/pyenv

To enable shims and autocompletion add to your profile:
  if which pyenv > /dev/null; then eval "$(pyenv init -)"; fi

They are obviously already in my .bash_profile file. The only necessary action is to do source ~/.bash_profile.

Problem solved.