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.
For your stated scenario, there is no reason to combine realpath and abspath, since os.path.realpath actually calls os.path.abspath before returning a result (I checked Python 2.5 to Python 3.6).
os.path.abspathreturns the absolute path, but does NOT resolve symlinks.os.path.realpathwill first resolve any symbolic links in the path, and then return the absolute path.
However, if you expect your path to contain a ~, neither abspath or realpath will resolve ~ to the user's home directory, and the resulting path will be invalid. You will need to use os.path.expanduser to resolve this to the user's directory.
For the sake of a thorough explanation, here are some results which I've verified in Windows and Linux, in Python 3.4 and Python 2.6. The current directory (./) is my home directory, which looks like this:
myhome
|- data (symlink to /mnt/data)
|- subdir (extra directory, for verbose explanation)# os.path.abspath returns the absolute path, but does NOT resolve symlinks
os.path.abspath('./')
'/home/myhome'
os.path.abspath('./subdir/../data')
'/home/myhome/data'
# os.path.realpath will resolve symlinks AND return an absolute path from a relative path
os.path.realpath('./')
'/home/myhome'
os.path.realpath('./subdir/../')
'/home/myhome'
os.path.realpath('./subdir/../data')
'/mnt/data'
# NEITHER abspath or realpath will resolve or remove ~.
os.path.abspath('~/data')
'/home/myhome/~/data'
os.path.realpath('~/data')
'/home/myhome/~/data'
# And the returned path will be invalid
os.path.exists(os.path.abspath('~/data'))
False
os.path.exists(os.path.realpath('~/data'))
False
# Use realpath + expanduser to resolve ~
os.path.realpath(os.path.expanduser('./subdir/../data'))
'/mnt/data'