title: Why python throws an "ImportError: No module named linkextractor" even if the Scrapy module already installed?
body: <p>I want to install <a href="https://github.com/scrapinghub/portia" rel="nofollow">portia</a>. It requires <code>scrapy</code> and <code>slybot</code>.
  I also installed <code>virtualenv</code> (as recommended) and executed <code>virtualenv Portia</code> to create a python virtual environment only for this project. Now it requires to start <code>twisted</code> server with <code>twistd -n slyd</code>, but then it throws an Error:</p>
  
  <pre><code>  File "/home/john/Downloads/portia-master/slybot/slybot/linkextractor/__init__.py", line 6, in &lt;module&gt;
      from .base import BaseLinkExtractor, ALLOWED_SCHEMES   File "/home/john/Downloads/portia-master/slybot/slybot/linkextractor/base.py", line 6, in &lt;module&gt;
      from scrapy.linkextractor import IGNORED_EXTENSIONS ImportError: No module named linkextractor
  </code></pre>
  
  <p>I have Ubuntu 12.04, installed: <code>python 2.7, pip, python-scrapy, python-twisted</code></p>
  
  <p>What could be here wrong? I didn't use <code>pip</code> and <code>virtualenv</code> before, does seem something wrong with the deployment workflow (e.g. ENVIRONMENT variables, other <code>virtualenv/pip</code> configurations) I described above?</p>