title: Half of anaconda3 has py27 build path
body: <p>While trying to install a particular package using conda, I didn't notice how many packages were going to be downgraded and foolishly gave the go-ahead. For the most part, the version numbers weren't downgraded, but they downgraded from a <code>py37</code> build channel to a <code>py27</code> build channel. Running <code>conda list</code> now gives me lines with a mix of py27 and py37:</p>
  
  <pre><code>jupyter                   1.0.0                    py37_7  
  jupyter_client            5.2.4                    py27_0  
  jupyter_console           5.2.0                    py27_1  
  jupyter_core              4.4.0                    py27_0  
  jupyterlab                0.35.3                   py37_0
  </code></pre>
  
  <p>I can't remember what it looked like before, but I don't believe I had this garbled mess of python2 and python3, as I haven't built anything with python2 into my conda. Running <code>conda update --all</code> doesn't resolve this, as I believe it only checks the version and not the build path. How can I change everything back to python3 and ideally remove all traces of python2?</p>
  
  <p><strong>Edit:</strong>
  The line in particular that caused this was <code>conda install -c menpo vtk=7</code> when trying to install <a href="http://daetools.com/docs/getting_daetools.html" rel="nofollow noreferrer">DAETools</a></p>