title: Set default python with pyenv
body: <p>I am try to upgrade my Python version on my macOS Catalina 10.15.1 by install PYENV and PYPIP, and set global and local to version 3.8.0. but still when I try to python version it shows the python version which  built into the MacOS operating system. which part is missing?</p>
  <pre><code>$ pyenv -v
  pyenv 1.2.14
  
  $ pypip -v
  zsh: command not found: pypip
  
  $ pyenv versions
    system
  * 3.8.0 (set by /Users/aj/.python-version)
  
  $ pyenv global
  3.8.0
  
  $ pyenv local
  3.8.0
  
  $ python -V
  Python 2.7.16
  </code></pre>