title: What's the difference between pip3 and pip?
body: <p>I know that <code>pip3</code> refers to <code>python3</code> and <code>pip</code> refers to <code>python2</code>. 
  When I use <code>anaconda</code> environment and set the <code>python</code> version as <code>3.5</code>, I install a package names <code>itchat</code> as following.</p>
  
  <pre><code>pip3 install itchat
  </code></pre>
  
  <p>The installation goes on successfully without any errors.</p>
  
  <p><strong>But</strong> when I type the following commands, strange things happen.
  <a href="https://i.stack.imgur.com/U0Rmy.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/U0Rmy.jpg" alt="enter image description here"></a></p>
  
  <p><strong>But</strong> if I just use <code>pip install itchat</code> and type <code>python</code> instead of <code>python3</code>, things go on as I think.
  <a href="https://i.stack.imgur.com/jG7NN.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/jG7NN.jpg" alt="enter image description here"></a></p>
  
  <p>I am wondering what leads to this result. 
  Why there is the difference between <code>python</code> and <code>python3</code>?</p>
  
  <p>Thanks for providing your answers!</p>