User memoize function throws warning

[destos]

Describe the bug
Whenever you run a command or do anything you gey a warning from the cache backend.

usr/local/lib/python3.7/site-packages/django/core/cache/backends/base.py:254: CacheKeyWarning: Cache key contains characters that will cause errors if used with memcached: ':1:toolhub_auth.models.User.has_clearance.<User: >_memver'

To Reproduce
Steps to reproduce the behavior:

1. Run any management command