This is a custom template filter that allows you to truncate a string to a maximum of num characters, but respecting word boundaries. So, for example, if `string = "This is a test string."`, then `{{ string|truncatechars:12 }}` would give you "This is a..." instead of "This is a te".
This is a fairly small bit template that, if placed in your_project_dir/templates/admin/prepopulated_fields_js.html will override the template that is normally pulled by the preopulated fields templatetag in the admin. The result is that you can successfully specify a ForeignKey or other field involving choices as a source for prepopulate_from in your admin.py. It works just as well when there are multiple fields of both the text and choice variety.
josho has posted 2 snippets.