title: pip: install dependencies of dependencies
body: <p>I would like to manually install all the requirements of a Python package I'm writing. To this end, I created the file <code>requirements.txt</code> and added the dependencies, line by line:</p>
  
  <pre><code>$ cat requirements.txt
  meshio
  numpy
  </code></pre>
  
  <p>When running</p>
  
  <pre><code>$ pip install -r requirements.txt
  </code></pre>
  
  <p>those two packages are installed alright, but I noticed that the dependencies of meshio aren't (i.e., whatever is listed in its <code>requirements.txt</code>). Not surprising, how is pip supposed to know?</p>
  
  <p>Is there a mechanism for installing the entire dependency tree with pip?</p>