title: pip or pip3 to install packages for Python 3?
body: <p>I have a Macbook with OS X El Captain. I think that Python 2.7 comes preinstalled on it. However, I installed Python 3.5 too. When I started using Python 3, I read that if I want to install a package, I should type:</p>
  <pre><code>pip3 install some_package
  </code></pre>
  <p>Anyway, now when I use</p>
  <pre><code>pip install some_package
  </code></pre>
  <p>I get <code>some_package</code> installed for Python 3. I mean I can import it and use it without problems. Moreover, when I type just <code>pip3</code> in the Terminal. I got this message about the usage:</p>
  <pre><code>Usage:   
    pip &lt;command&gt; [options]
  </code></pre>
  <p>which is the same message I get when I type just <code>pip</code>.</p>
  <p>Does it mean that in previous versions, things were different, and now <code>pip</code> and <code>pip3</code> can be used interchangeably? If so, and for the sake of argument, how can I install packages for Python 2 instead of Python 3?</p>