title: Homebrew python3 installation error
body: <p>I was trying to install python 3 using Homebrew by doing <code>brew install python3</code> and  there was the warning.</p>
  
  <p>Warning: The post-install step did not complete successfully
  You can try again using <code>brew postinstall python3</code></p>
  
  <p>So I did instead do  <code>brew postinstall python3</code></p>
  
  <p>```==> /usr/local/Cellar/python3/3.4.1/bin/python3 -m ensurepip --upgrade
  dyld: Library not loaded: @@HOMEBREW_CELLAR@@/python3/3.4.1/Frameworks/Python.framework/Versions/3.4/Python
    Referenced from: /usr/local/Cellar/python3/3.4.1/bin/python3
    Reason: image not found
  xcrun: error: active developer path ("/Users/dorislee/Desktop/Macintosh HD/Applications/Xcode.app/Contents/Developer") does not exist, use xcode-select to change
  xcrun: error: active developer path ("/Users/dorislee/Desktop/Macintosh HD/Applications/Xcode.app/Contents/Developer") does not exist, use xcode-select to change</p>
  
  <p>READ THIS: <a href="https://github.com/Homebrew/homebrew/wiki/troubleshooting" rel="nofollow">https://github.com/Homebrew/homebrew/wiki/troubleshooting</a>```</p>
  
  <p>I am not really sure what to do, is there a way to undo this and fix it?</p>