title: run Django server by calling subprocess from another Django project
body: <p>I have two Django projects, <code>foo</code> and <code>bar</code>, and the structures are shown in the following.</p>
  
  <pre><code>/tmp/foo
    - foo
      - __init__.py
      - settings.py
      - urls.py
      - wsgi.py
  
  /tmp/bar
    - bar
      - __init__.py
      - settings.py
      - urls.py
      - wsgi.py
  </code></pre>
  
  <p>I tried to run <code>python3 /tmp/bar/manage.py runserver</code> in <code>foo</code>'s environment but failed.</p>
  
  <pre><code>$ python3 /tmp/foo/manage.py shell
  
  &gt;&gt;&gt; import subprocess
  &gt;&gt;&gt; subprocess.call(['python3', '/tmp/bar/manage.py', 'runserver'])
  
  Traceback (most recent call last):
    File "/tmp/bar/manage.py", line 10, in &lt;module&gt;
      execute_from_command_line(sys.argv)
    File "/usr/local/lib/python3.4/dist-packages/django/core/management/__init__.py", line 353, in execute_from_command_line
      utility.execute()
    File "/usr/local/lib/python3.4/dist-packages/django/core/management/__init__.py", line 302, in execute
      settings.INSTALLED_APPS
    File "/usr/local/lib/python3.4/dist-packages/django/conf/__init__.py", line 55, in __getattr__
      self._setup(name)
    File "/usr/local/lib/python3.4/dist-packages/django/conf/__init__.py", line 43, in _setup
      self._wrapped = Settings(settings_module)
    File "/usr/local/lib/python3.4/dist-packages/django/conf/__init__.py", line 99, in __init__
      mod = importlib.import_module(self.SETTINGS_MODULE)
    File "/usr/lib/python3.4/importlib/__init__.py", line 109, in import_module
      return _bootstrap._gcd_import(name[level:], package, level)
    File "&lt;frozen importlib._bootstrap&gt;", line 2254, in _gcd_import
    File "&lt;frozen importlib._bootstrap&gt;", line 2237, in _find_and_load
    File "&lt;frozen importlib._bootstrap&gt;", line 2212, in _find_and_load_unlocked
    File "&lt;frozen importlib._bootstrap&gt;", line 321, in _call_with_frames_removed
    File "&lt;frozen importlib._bootstrap&gt;", line 2254, in _gcd_import
    File "&lt;frozen importlib._bootstrap&gt;", line 2237, in _find_and_load
    File "&lt;frozen importlib._bootstrap&gt;", line 2224, in _find_and_load_unlocked
  ImportError: No module named 'foo'
  1
  </code></pre>
  
  <p>How can I resolve this?  </p>
  
  <p>(I know this behavior doesn't make sense at all, but this is just for the demonstration purpose only.)</p>