title: Get the requirements of a package in PyPI without installing it?
body: <p>I need something like the following:</p>
  
  <pre><code>pip showrequirements tensorflow
  </code></pre>
  
  <p>This would return something that allows me to parse the names of the required packages and the required versions:</p>
  
  <pre><code>astor&gt;0.6, tensorboard&gt;1.0.11, etc.
  </code></pre>
  
  <p>pip is getting this information in some form during the install and download command. I can see where it's happening in the code... but before I hack my way to using pip's internal code, is there any easy API or existing library that can do this? </p>
  
  <p>edit: I cannot install the package to see this, so pip show won't work. One (hacky) solution is parsing the output of pip download.</p>
  
  <p>Thanks!</p>