title: How to `pip install` a package that has Git dependencies?
body: <p>I have a private library called <code>some-library</code> <em>(actual names have been changed)</em> with a setup file looking somewhat like this:</p>
  
  <pre><code>setup(
      name='some-library',
  
      // Omitted some less important stuff here...
  
      install_requires=[
          'some-git-dependency',
          'another-git-dependency',
      ],
      dependency_links=[
          'git+ssh://git@github.com/my-organization/some-git-dependency.git#egg=some-git-dependency',
          'git+ssh://git@github.com/my-organization/another-git-dependency.git#egg=another-git-dependency',
      ],
  )
  </code></pre>
  
  <p>All of these Git dependencies <em>may</em> be private, so <a href="https://stackoverflow.com/a/14928126/4101697">installation via HTTP</a> is not an option. I can use <code>python setup.py install</code> and <code>python setup.py develop</code> in <code>some-library</code>'s root directory without problems.</p>
  
  <p>However, installing over Git doesn't work:</p>
  
  <pre><code>pip install -vvv -e 'git+ssh://git@github.com/my-organization/some-library.git@1.4.4#egg=some-library'
  </code></pre>
  
  <p>The command fails when it looks for <code>some-git-dependency</code>, mistakenly assumes it needs to get the dependency from PyPI and then fails after concluding it's not on PyPI. My first guess was to try re-running the command with <code>--process-dependency-links</code>, but then this happened:</p>
  
  <pre><code>   Cannot look at git URL git+ssh://git@github.com/my-organization/some-git-dependency.git#egg=some-git-dependency
     Could not find a version that satisfies the requirement some-git-dependency (from some-library) (from versions: )
  </code></pre>
  
  <p>Why is it producing this vague error? What's the proper way to <code>pip install</code> a package with Git dependencies that might be private?</p>