title: How to install Numpy & pip3 for python3.x when they were installed in python2.7? Using Conda?
body: <p>I want to write program in python3 (3.5), hence I installed python3 next to the pre-installed python2 (2.7) on Mac OS X El Captian.</p>
  
  <p>Since my terminal runs python2.7 by default and Numpy is already installed for it, I put <code>alias python=python3</code> and expected to be able to install Numpy for python3. when I type <code>pip install numpy</code>. This was the generated message:</p>
  
  <pre><code>Requirement already satisfied (use --upgrade to upgrade): numpy in /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages
  </code></pre>
  
  <p>I also noticed that I have no <code>pip3</code> even though I am using python3: <code>python --version</code> returned <code>Python 3.5.2</code>, but <code>pip3 install numpy</code> got me <code>-bash: pip3: command not found</code>. </p>
  
  <p>So my questions are:<br>
  1) How to install Numpy for python3.x when Numpy is installed on python2.x?<br>
  2) How to get pip3?<br>
  3) Is it better to use virtual environments, such as Conda, instead of juggling between python2 and python3 on the system?</p>
  
  <p>Thank you from a total n00b</p>
  
  <p><strong>------------------- Update -------------------</strong>  </p>
  
  <p>Reinstalling python3 also fixed another problem in my case.<br>
  When I ran <code>brew doctor</code>, one of the warning message I got was:</p>
  
  <p><code>Warning: You have unlinked kegs in your Cellar Leaving kegs unlinked can lead to build-trouble and cause brews that depend on those kegs to fail to run properly once built. Run brew link on these: python –</code></p>
  
  <p>This is a result of me running <code>brew unlink python</code> in order to fix </p>
  
  <blockquote>
    <p>"Python quit unexpectedly"</p>
  </blockquote>
  
  <p>when I launch Vim and also </p>
  
  <blockquote>
    <p>"The ycmd server SHUT DOWN"</p>
  </blockquote>
  
  <p>Both seem to relate to the YouCompleteMe autocomplete plugin which I downloaded for Python. </p>
  
  <p>I got my idea of removing symlinks from <a href="https://github.com/Valloric/YouCompleteMe/issues/585" rel="nofollow">here</a> and <a href="https://github.com/Valloric/YouCompleteMe/issues/611" rel="nofollow">here</a><br>
  However, Homebrew evidently did not like the absence of those 39 symlinks.</p>
  
  <p>After uninstall (<code>brew uninstall python3</code>) and then re-install python3 (<code>brew install python3</code>) as Toby suggested, Homebrew gave me </p>
  
  <pre><code>You can install Python packages with  
  pip3 install &lt;package&gt;
  </code></pre>
  
  <p>Then when I <code>pip3 install numpy</code> and <code>pip3 install scipy</code>, both executed successfully.</p>
  
  <p>To my surprise, symlinks created during Python installation used to cause aforementioned error messages for Python and YouCompleteMe, but now I open python files using Vim without crash from a fresh Python installation, which definitely created the symlinks. </p>
  
  <p><strong>------------------- Update2 ------------------</strong></p>
  
  <p>After re-installing Anaconda2, the same YouCompleteMe error came back. I suspect Anaconda messed up symlinks.</p>