PIP Constraints Files
<p>I was reading the <a href="https://pip.pypa.io/en/stable/user_guide/#constraints-files" rel="noreferrer">docs</a> and couldn't wrap my head around it:</p>
<blockquote>
<p>Constraints files are requirements files that only control which
version of a requirement is installed, not whether it is installed or
not. Their syntax and contents is nearly identical to Requirements
Files.</p>
<p>There is one key difference: Including a package in a constraints file
does not trigger installation of the package.</p>
</blockquote>
<ul>
<li>So does that mean I need to requirement files first then run constraint?</li>
<li>Need to have both requirements.txt and constraints.txt?</li>
<li>Or just <code>-c requirements.txt</code>?</li>
</ul>
<p>Could someone please explain in plain English that what the new PIP feature: <strong>Constraints Files</strong> does?</p>