title: pip freeze creates some weird path instead of the package version
body: <p>I am working on developing a python package. I use <code>pip freeze &gt; requirements.txt</code> to add the required package into the requirement.txt file. However, I realized that some of the packages, instead of the package version, have some path in front of them.</p>
  <pre><code>numpy==1.19.0
  packaging==20.4
  pandas @ file:///opt/concourse/worker/volumes/live/38d1301c-8fa9-4d2f-662e-34dddf33b183/volume/pandas_1592841668171/work
  pandocfilters==1.4.2
  </code></pre>
  <p>Whereas, inside the environment, I get:</p>
  <pre><code>&gt;&gt;&gt; pandas.__version__
  '1.0.5'
  </code></pre>
  <p>Do you have any idea how to address this problem?</p>