title: How to efficiently manage frequent schema changes using sqlalchemy?
body: <p>I'm programming a web application using sqlalchemy. Everything was smooth during the first phase of development when the site was not in production. I could easily change the database schema by simply deleting the old sqlite database and creating a new one from scratch. </p>
  
  <p>Now the site is in production and I need to preserve the data, but I still want to keep my original development speed by easily converting the database to the new schema. </p>
  
  <p>So let's say that I have model.py at revision 50 and model.py a revision 75, describing the schema of the database. Between those two schema most changes are trivial, for example a new column is declared with a default value and I just want to add this default value to old records. </p>
  
  <p>Eventually a few changes may not be trivial and require some pre-computation. </p>
  
  <p>How do (or would) you handle fast changing web applications with, say, one or two new version of the production code per day  ?</p>
  
  <p>By the way, the site is written in Pylons if this makes any difference.</p>