How to get an absolute file path in Python

You could use the new Python 3.4 library pathlib. (You can also get it for Python 2.6 or 2.7 using pip install pathlib.) The authors wrote: "The aim of this library is to provide a simple hierarchy of classes to handle filesystem paths and the common operations users do over them."

To get an absolute path in Windows:

>>> from pathlib import Path
>>> p = Path("pythonw.exe").resolve()
>>> p
WindowsPath('C:/Python27/pythonw.exe')
>>> str(p)
'C:\\Python27\\pythonw.exe'

Or on UNIX:

>>> from pathlib import Path
>>> p = Path("python3.4").resolve()
>>> p
PosixPath('/opt/python3/bin/python3.4')
>>> str(p)
'/opt/python3/bin/python3.4'

Docs are here: https://docs.python.org/3/library/pathlib.html

Better still, install the module (found on PyPI), it wraps all the os.path functions and other related functions into methods on an object that can be used wherever strings are used:

>>> from path import path
>>> path('mydir/myfile.txt').abspath()
'C:\\example\\cwd\\mydir\\myfile.txt'
>>>

Today you can also use the unipath package which was based on path.py: http://sluggo.scrapping.cc/python/unipath/

>>> from unipath import Path
>>> absolute_path = Path('mydir/myfile.txt').absolute()
Path('C:\\example\\cwd\\mydir\\myfile.txt')
>>> str(absolute_path)
C:\\example\\cwd\\mydir\\myfile.txt
>>>

I would recommend using this package as it offers a clean interface to common os.path utilities.

Update for Python 3.4+ pathlib that actually answers the question:

from pathlib import Path

relative = Path("mydir/myfile.txt")
absolute = relative.absolute()  # absolute is a Path object

If you only need a temporary string, keep in mind that you can use Path objects with all the relevant functions in os.path, including of course abspath:

from os.path import abspath

absolute = abspath(relative)  # absolute is a str object

import os
os.path.abspath(os.path.expanduser(os.path.expandvars(PathNameString)))

Note that expanduser is necessary (on Unix) in case the given expression for the file (or directory) name and location may contain a leading ~/(the tilde refers to the user's home directory), and expandvars takes care of any other environment variables (like $HOME).