Why would one use both, os.path.abspath and os.path.realpath?

Question

In multiple open source projects, I have seen people do os.path.abspath(os.path.realpath(__file__)) to get the absolute path to the current file.

Howeve

Answer 1

os.path.realpath derefences symbolic links on those operating systems which support them.

os.path.abspath simply removes things like . and .. from the path giving a full path from the root of the directory tree to the named file (or symlink)

For example, on Ubuntu

$ ls -l
total 0
-rw-rw-r-- 1 guest guest 0 Jun 16 08:36 a
lrwxrwxrwx 1 guest guest 1 Jun 16 08:36 b -> a

$ python
Python 2.7.11 (default, Dec 15 2015, 16:46:19) 
[GCC 4.8.4] on linux2
Type "help", "copyright", "credits" or "license" for more information.

>>> from os.path import abspath, realpath

>>> abspath('b')
'/home/guest/play/paths/b'

>>> realpath('b')
'/home/guest/play/paths/a'

Symlinks can contain relative paths, hence the need to use both. The inner call to realpath might return a path with embedded .. parts, which abspath then removes.