ubuntu 12.10から13.04へのアップグレードを行い、virtualenvでdjangoサイトを実行しているときにこれを取得しました
(virtualenv)sysadmin@ubuntu:~/webapps/devsite/djangosite$ ./manage.py runserver
Traceback (most recent call last):
File "./manage.py", line 2, in <module>
from django.core.management import execute_manager
File "/home/sysadmin/webapps/devsite/virtualenv/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 7, in <module>
from django.core.management.base import BaseCommand, CommandError, handle_default_options
File "/home/sysadmin/webapps/devsite/virtualenv/local/lib/python2.7/site-packages/django/core/management/base.py", line 14, in <module>
from django.utils.encoding import smart_str
File "/home/sysadmin/webapps/devsite/virtualenv/local/lib/python2.7/site-packages/django/utils/encoding.py", line 4, in <module>
import datetime
ImportError: No module named datetime