Problem with import is that it:
- Reuses already-imported module.
For example, --settings-file=/etc/zerobin.py won't be imported,
because sys.modules will already contain 'zerobin' entry.
- Alters sys.path.
Importing module from a heavily-populated directory may potentially
cause next imports to run code from totally unexpected places.
Using execfile() doesn't set some globals like __file__ as import does,
which has to be done manually.
It also might be a bit slower for large body of code in settings file.
runpy.run_path() can only be used on python-2.7, but does not seem
to have any downsides.