title: Difference "pip wheel" and "pip download"?
body: <p>I'm trying to figure out what's the difference between these two python commands:</p>
  <pre><code>pip wheel --wheel-dir=some_dir -r requirement.txt
  </code></pre>
  <p>and</p>
  <pre><code>pip download -d some_dir -r requirement.txt
  </code></pre>
  <p>At first I thought &quot;pip download&quot; by default downloads the requirements from pypi.org index in 'whl' format and places them in some_dir, while &quot;pip wheel&quot; 'extracts' and builds the requirements, still in 'whl' format, from the current python environment and places them in some_dir.
  But apparently what both of them do is downloading the dependencies from the pypi.org index (by default).
  In fact, I tried the &quot;pip wheel&quot; command on an (virtual)python environment which didn't have installed any of the 'requirements.txt', yet still all of the 'whl's were found in 'some_dir'. The official documentation doesn't state this very clearly, though.</p>
  <p>Hence my questions:</p>
  <ol>
  <li>Are then the two commands equivalent? (In this case this would look like replication of instructions, not really a good design principle uncle Guido!)</li>
  <li>How can I achieve my goal of obtaining the whls required out of my python environment and ignoring any internet 'index's? (Suppose I've installed a module in a venv as obtained from pypi.org, then I customize that module and I need to bring those modifications in every new cloned venv environment, created with the customized whl module file)</li>
  </ol>
  <p>Thanks in advance!</p>