FOR THE RECORD, I'M **NOT** HOLDING THIS PULL REQUEST BACK BECAUSE OF THIS. I'M PERFECTLY AWARE THIS IS A NIT. 

Let's not get into no flame war here but another advantage I often feel about module level imports is that it's less burden on the future diffs. If you, at a later time, decide that your code also needs `timedelta` you only need one more change in the diff. E.g.
```
-from datetime import datetime
+from datetime import datetime, timedelta
...
print datetime(2013,1,1)
+print timedelta(days=1)
```
versus
```
import datetime
...
print datetime.datetime(2013,1,1)
+print datetime.timedelta(days=1)
```

So, by keeping it module level your diffs are less invasive.