title: Why does pip freeze list "pkg-resources==0.0.0"?
body: <p>On Ubuntu 16.04 with virtualenv 15.0.1 and Python 3.5.2 (both installed with <code>apt</code>) when I create and activate new Python virtual environment with</p>
  
  <pre class="lang-sh prettyprint-override"><code>virtualenv .virtualenvs/wtf -p $(which python3) --no-site-packages
  source .virtualenvs/wtf/bin/activate
  </code></pre>
  
  <p>I get the following output:</p>
  
  <pre class="lang-none prettyprint-override"><code>Already using interpreter /usr/bin/python3
  Using base prefix '/usr'
  New python executable in /home/das-g/.virtualenvs/wtf/bin/python3
  Also creating executable in /home/das-g/.virtualenvs/wtf/bin/python
  Installing setuptools, pkg_resources, pip, wheel...done.
  </code></pre>
  
  <p>Indeed <code>pip freeze --all</code> lists these 4 packages:</p>
  
  <pre><code>pip==8.1.2
  pkg-resources==0.0.0
  setuptools==25.2.0
  wheel==0.29.0
  </code></pre>
  
  <p>Though, I'd expect <code>pip freeze</code> (without <code>--all</code>) to omit these implicitly installed packages. It does omit some of them, but not <code>pkg-resources</code>:</p>
  
  <pre><code>pkg-resources==0.0.0
  </code></pre>
  
  <p>(Same btw. for <code>pip freeze --local</code>)</p>
  
  <p>While this is consistent with the help text</p>
  
  <pre class="lang-sh prettyprint-override"><code>$&gt; pip freeze --help | grep '\--all'
    --all                       Do not skip these packages in the output: pip, setuptools, distribute, wheel
  </code></pre>
  
  <p>having <code>pkg-resources</code> in the <code>pip freeze</code> output doesn't seem very useful and might even be harmful. (I suspect it's why running <code>pip-sync</code> from <a href="https://github.com/nvie/pip-tools">pip-tools</a> uninstalls pkg-resources from the virtual environment, subtly breaking the environment thereby.) <strong>Is there any good reason why <code>pip freeze</code> lists <code>pkg-resources</code> instead of omitting it, too?</strong> As far as I remember, it didn't list it on Ubuntu 14.04 (with Python 3.4).</p>