title: Auto Generating Migrations using alembic
body: <p>In the tutorial:
  <a href="http://alembic.readthedocs.org/en/latest/tutorial.html" rel="noreferrer">http://alembic.readthedocs.org/en/latest/tutorial.html</a>
  I tested Auto Generating Migrations function by below command:</p>
  
  <pre><code>alembic revision --autogenerate -m "Added account table"
  </code></pre>
  
  <p>and got error:</p>
  
  <pre><code>Traceback (most recent call last):
  File "/usr/local/bin/alembic", line 9, in &lt;module&gt;
  load_entry_point('alembic==0.3.4', 'console_scripts', 'alembic')()
  File "/usr/local/lib/python2.7/dist-packages/alembic-0.3.4-py2.7.egg/alembic/config.py", line 229, in main
   **dict((k, getattr(options, k)) for k in kwarg)
  File "/usr/local/lib/python2.7/dist-packages/alembic-0.3.4-py2.7.egg/alembic/command.py", line 93, in  revision
  script.run_env()
  File "/usr/local/lib/python2.7/dist-packages/alembic-0.3.4-py2.7.egg/alembic/script.py", line 188, in run_env
   util.load_python_file(self.dir, 'env.py')
  File "/usr/local/lib/python2.7/dist-packages/alembic-0.3.4-py2.7.egg/alembic/util.py", line 185, in load_python_file
  module = imp.load_source(module_id, path, open(path, 'rb'))
  File "alembic/env.py", line 20, in &lt;module&gt;
  from myapp.mymodel import Base
  ImportError: No module named myapp.mymodel
  </code></pre>
  
  <p>I am just learning alembic, and also have never used python. Is the myapp.mymodel already there, or I need to create that using python. How to do that? Thank you very much!</p>