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

When setting Environmental Variables in Windows, I have gone wrong on many, many occasions. I thought I should share a few of my past mistakes here hoping that it might help someone. (These apply to all Environmental Variables, not just when setting Python Path)

Watch out for these possible mistakes:

1. Kill and reopen your shell window: Once you make a change to the ENVIRONMENTAL Variables, you have to restart the window you are testing it on.
2. NO SPACES when setting the Variables. Make sure that you are adding the ;C:\Python27 WITHOUT any spaces. (It is common to try C:\SomeOther; C:\Python27 That space (␣) after the semicolon is not okay.)
3. USE A BACKWARD SLASH when spelling out your full path. You will see forward slashes when you try echo $PATH but only backward slashes have worked for me.
4. DO NOT ADD a final backslash. Only C:\Python27 NOT C:\Python27\