title: Alembic: alembic revision says Import Error
body: <p>I am trying to integrate my <code>Flask</code> project with <code>Alembic</code><br>
  My application structure looks like</p>
  
  <pre><code>project/
         configuration/
                      __init__.py
                      dev.py
                      test.py
         core/
             # all source code
         db/
           migrations/
                      __init__.py
                      alembic.ini
                      env.py
                      versions/
  </code></pre>
  
  <p>When I try to run the following from my <code>db</code> directory, I see</p>
  
  <pre><code> File "migration/env.py", line 55, in run_migrations_online
      from configuration import app, db
  ImportError: No module named configuration
  </code></pre>
  
  <p>I tried the solution mentioned in <a href="https://stackoverflow.com/questions/11276017/request-a-simple-alembic-working-example-for-auto-generating-migrations">Request a simple alembic working example for Auto Generating Migrations</a>, but it does not work for me</p>
  
  <p>My method in <code>env.py</code> <code>run_migrations_online()</code> with change is</p>
  
  <pre><code>def run_migrations_online():
      """Run migrations in 'online' mode.
  
      In this scenario we need to create an Engine
      and associate a connection with the context.
  
      """
      import os
      import sys
  
      sys.path.append(os.getcwd())
      from configuration import app, db
  
      alembic_config = config.get_section(config.config_ini_section)
      alembic_config['sqlalchemy.url'] = app.config['SQLALCHEMY_DATABASE_URI']
      target_metadata = db.metadata
  
      engine = engine_from_config(
          alembic_config,
          prefix='sqlalchemy.',
          poolclass=pool.NullPool)
  
      connection = engine.connect()
      context.configure(
          connection=connection,
          target_metadata=target_metadata
      )
  
      try:
          with context.begin_transaction():
              context.run_migrations()
      finally:
          connection.close()
  
  
  if context.is_offline_mode():
      run_migrations_offline()
  else:
      run_migrations_online()
  </code></pre>
  
  <p>How can I fix this?</p>