It's not a requirement, but it will make me happier to look at your code if you mostly use `format` instead of string concatenation with `+`.  I like this because it is more like a template and I find it easier to parse.  This also makes it easier to not have over-long lines like this.  So e.g.
```
return '{0}\nSee {1}'.format(
    super(Exception, self),
    'http://irsa.ipac.caltech.edu/applications/DDGEN/Doc/DBMSrestriction.html')
```