Built-in Python modules should always be at the top of the import list.

Imports live in three groups, each separated by a blank line:

1) Built-in Python modules
2) Third-party Python modules not part of the current project
3) Python modules part of the current project.

They should be alphabetical.

When doing string comparisons against "", you can do:

if not review_request.submitter.first_name:

You probably don't want this check, though. We want to verify the text regardless.

"signature"

lines should always be less than 80 columns long.

However, you shouldn't deal with with first_name and last_name themselves. Since the e-mail template may also generate a username, what you really want is our utility function, user_displayname.

For that, you'll have to do:

from djblets.util.templatetags.djblets_utils import user_displayname

...

signature = 'Thanks.\n\n%s' % user_displayname(review_request.submitter)

This whole line should actually be:

{{review_request.submitter|user_displayname}}