The log message should be fixed and the `extra` argument can be used to pass the variables. This is so log aggregators (such as Sentry) can bin them together of the same type.

```python
log.error('Concept has orphaned field', extra={
    'concept': concept.pk,
    'field': field.pk,
})
```

_See more about the [extra agument](http://docs.python.org/2/library/logging.html#logging.Logger.debug)_