title: Python relative import syntax: `from . import abc.xyz`
body: <p><strong>Issue:</strong> I am trying to install <a href="https://github.com/openx/python3-protobuf" rel="nofollow noreferrer">a Python3 port of Google Protocol Buffers</a>. When I do a <code>python3 setup.py test</code> I get the following error:</p>
  
  <pre><code>    File "/[*snip*]/python3-protobuf-master/python/google/protobuf/unittest_custom_options_pb2.py", line 13
      from . import google.protobuf.descriptor_pb2
                          ^
  SyntaxError: invalid syntax
  </code></pre>
  
  <p>I then tried similar syntax in both my Python3 and Python2 interpreters and got the same error:</p>
  
  <pre><code>Python 3.2.3 (default, Jul 23 2012, 16:48:24)
  [GCC 4.5.3] on cygwin
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; from . import x.y
    File "&lt;stdin&gt;", line 1
      from . import x.y
                     ^
  SyntaxError: invalid syntax
  </code></pre>
  
  <p><strong>Question:</strong> When is <code>from . import abc.xyz</code> valid Python syntax, if at all? I am interested in knowing if this code I downloaded is inherently malformed.</p>
  
  <p><strong>Misc:</strong> I chose this Python3 port of GPB from an answer on <a href="https://stackoverflow.com/questions/8663468/is-there-any-way-to-access-protocol-buffers-with-python-3-x">this SO question.</a> It  is not up-to-date with regard to GPB, but I expected it to still function. Let me know if you know better about Python3 ports of GPB.</p>