title: What is pip's equivalent of `npm install package --save-dev`?
body: <p>In nodejs, I can do <code>npm install package --save-dev</code> to save the installed package into the package.</p>
  
  <p>How do I achieve the same thing in Python package manager <code>pip</code>? I would like to save the package name and its version into, say, <code>requirements.pip</code> just after installing the package using something like <code>pip install package --save-dev requirements.pip</code>.</p>