Should use abspath for default settings.BASE_DIR

[Harry Percival]

ref the default project template's settings.py, BASE_DIR is defined as:

BASE_DIR = os.path.dirname(os.path.dirname(__file__))

Because there's no abspath, you can get different results for BASE_DIR depending on how settings.py is run. This is an edge case, since settings.py is almost always imported by django in the right context, but still -- compare:

    python manage.py shell
    >>> from django.conf import settings
    print(BASE_DIR)

With:

    python -i myproject/settings.py
    >>> print(BASE_DIR)

As an aside, in general, in any path wrangling you should always call abspath first. Try running this script, saved to a file:

import os
print(os.path.abspath(os.path.dirname(os.path.dirname(file))))
print(os.path.dirname(os.path.dirname(os.path.abspath(file))))

As to tests, the only one I can think of would be a pretty horrible one involving actually callling out using subprocess.Popen to a python -i of the project template settings file, so maybe ok not to bother?

credit to @CleanCut for turning me onto this weirdness!