When using try/except it's generally a good practice:
 1. Catch a single exception on every `except`, so you can handle the exception accordingly and avoid silencing exception that you didn't expect.
 2. Limit the lines in try/except to minimum.

In this case I imagine that you want to catch the `ValidationError`s that can be raised from `validate_twitter`, so the code should be like this

```python
try:
   twitter_username = validate_twitter(u.identifier)
except ValidationError as exception:
   print exception
   continue
u.identifier = twitter_username
u.save()
```