The OP specified "will work with Windows paths too". There are a few wrinkles with Windows paths.

Firstly, Windows has the concept of multiple drives, each with its own current working directory, and 'c:foo' and 'c:\\foo' are often not the same. Consequently it is a very good idea to separate out any drive designator first, using os.path.splitdrive(). Then reassembling the path (if required) can be done correctly by drive + os.path.join(*other_pieces)

Secondly, Windows paths can contain slashes or backslashes or a mixture. Consequently, using os.sep when parsing an unnormalised path is not useful.

More generally:

The results produced for 'foo' and 'foo/' should not be identical.

The loop termination condition seems to be best expressed as "os.path.split() treated its input as unsplittable".

Here's a suggested solution, with tests, including a comparison with @Spacedman's solution

import os.path

def os_path_split_asunder(path, debug=False):
    parts = []
    while True:
        newpath, tail = os.path.split(path)
        if debug: print repr(path), (newpath, tail)
        if newpath == path:
            assert not tail
            if path: parts.append(path)
            break
        parts.append(tail)
        path = newpath
    parts.reverse()
    return parts

def spacedman_parts(path):
    components = [] 
    while True:
        (path,tail) = os.path.split(path)
        if not tail:
            return components
        components.insert(0,tail)

if __name__ == "__main__":
    tests = [
        '',
        'foo',
        'foo/',
        'foo\\',
        '/foo',
        '\\foo',
        'foo/bar',
        '/',
        'c:',
        'c:/',
        'c:foo',
        'c:/foo',
        'c:/users/john/foo.txt',
        '/users/john/foo.txt',
        'foo/bar/baz/loop',
        'foo/bar/baz/',
        '//hostname/foo/bar.txt',
        ]
    for i, test in enumerate(tests):
        print "\nTest %d: %r" % (i, test)
        drive, path = os.path.splitdrive(test)
        print 'drive, path', repr(drive), repr(path)
        a = os_path_split_asunder(path)
        b = spacedman_parts(path)
        print "a ... %r" % a
        print "b ... %r" % b
        print a == b

and here's the output (Python 2.7.1, Windows 7 Pro):

Test 0: ''
drive, path '' ''
a ... []
b ... []
True

Test 1: 'foo'
drive, path '' 'foo'
a ... ['foo']
b ... ['foo']
True

Test 2: 'foo/'
drive, path '' 'foo/'
a ... ['foo', '']
b ... []
False

Test 3: 'foo\\'
drive, path '' 'foo\\'
a ... ['foo', '']
b ... []
False

Test 4: '/foo'
drive, path '' '/foo'
a ... ['/', 'foo']
b ... ['foo']
False

Test 5: '\\foo'
drive, path '' '\\foo'
a ... ['\\', 'foo']
b ... ['foo']
False

Test 6: 'foo/bar'
drive, path '' 'foo/bar'
a ... ['foo', 'bar']
b ... ['foo', 'bar']
True

Test 7: '/'
drive, path '' '/'
a ... ['/']
b ... []
False

Test 8: 'c:'
drive, path 'c:' ''
a ... []
b ... []
True

Test 9: 'c:/'
drive, path 'c:' '/'
a ... ['/']
b ... []
False

Test 10: 'c:foo'
drive, path 'c:' 'foo'
a ... ['foo']
b ... ['foo']
True

Test 11: 'c:/foo'
drive, path 'c:' '/foo'
a ... ['/', 'foo']
b ... ['foo']
False

Test 12: 'c:/users/john/foo.txt'
drive, path 'c:' '/users/john/foo.txt'
a ... ['/', 'users', 'john', 'foo.txt']
b ... ['users', 'john', 'foo.txt']
False

Test 13: '/users/john/foo.txt'
drive, path '' '/users/john/foo.txt'
a ... ['/', 'users', 'john', 'foo.txt']
b ... ['users', 'john', 'foo.txt']
False

Test 14: 'foo/bar/baz/loop'
drive, path '' 'foo/bar/baz/loop'
a ... ['foo', 'bar', 'baz', 'loop']
b ... ['foo', 'bar', 'baz', 'loop']
True

Test 15: 'foo/bar/baz/'
drive, path '' 'foo/bar/baz/'
a ... ['foo', 'bar', 'baz', '']
b ... []
False

Test 16: '//hostname/foo/bar.txt'
drive, path '' '//hostname/foo/bar.txt'
a ... ['//', 'hostname', 'foo', 'bar.txt']
b ... ['hostname', 'foo', 'bar.txt']
False

I've been bitten loads of times by people writing their own path fiddling functions and getting it wrong. Spaces, slashes, backslashes, colons -- the possibilities for confusion are not endless, but mistakes are easily made anyway. So I'm a stickler for the use of os.path, and recommend it on that basis.

(However, the path to virtue is not the one most easily taken, and many people when finding this are tempted to take a slippery path straight to damnation. They won't realise until one day everything falls to pieces, and they -- or, more likely, somebody else -- has to work out why everything has gone wrong, and it turns out somebody made a filename that mixes slashes and backslashes -- and some person suggests that the answer is "not to do that". Don't be any of these people. Except for the one who mixed up slashes and backslashes -- you could be them if you like.)

You can get the drive and path+file like this:

drive, path_and_file = os.path.splitdrive(path)

Get the path and the file:

path, file = os.path.split(path_and_file)

Getting the individual folder names is not especially convenient, but it is the sort of honest middling discomfort that heightens the pleasure of later finding something that actually works well:

folders = []
while 1:
    path, folder = os.path.split(path)

    if folder != "":
        folders.append(folder)
    else:
        if path != "":
            folders.append(path)

        break

folders.reverse()

(This pops a "\" at the start of folders if the path was originally absolute. You could lose a bit of code if you didn't want that.)

You can try using str.format to have variable filenames

Ex:

import pathlib
filename = "other_file.dat"    #Variable. 
path = pathlib.Path("/home/user/to/some/floder/{0}".format(filename))