title: IPython 3.5 returns "bad interpreter: No such file or directory"
body: <p>I am getting random error while trying to use IPython. I now suddenly cannot use iPython3 with no explanation, I don't remember installing anything heavy besides Ethereum client and I didn't download the hashes or anything.  Suddenly I get:</p>
  
  <pre><code>cchilders:~ 
  $ ipython3
  -bash: /usr/local/bin/ipython3: /usr/local/opt/python3/bin/python3.5: bad interpreter: No such file or directory
  </code></pre>
  
  <p>neither IPython or IPython3 was working. After uninstalling and reinstalling Python and Python3, I can now use IPython. But the same error from before happens if I try iPython3.</p>
  
  <p>This is one of the more absurd errors I've seen because I've reinstalled IPython, Python itself, and Python3 with no change.</p>