Check if a directory is a (file system) root

Question

I have a script that searches for a directory containing a specific file, starting from the current directory and going up the tree (think of trying to find out where the .git directory sits).

My method looks like this:

def getDir(self,cwd):
  path = os.path.abspath(cwd)
  if not os.path.isdir(path):
    raise RuntimeError("getDir should not be run on files")
  if FILE in os.listdir(path):
    return path
  parent = os.path.join(path, os.path.pardir)
  if os.access(parent, os.R_OK) and os.access(parent, os.X_OK):
    return self.getDir(parent)
  else
    return None

Now the problem with this method is that, if it cannot find the directory, it loops (and eventually stack-overflows) because apparently joining / and .. gives you / again. I tried comparing path with parent or their reprs, but that did not work (they were always distinct). My workaround for now is to include a depth counter in the recursive method and stop at some random maximum threshold.

My question is thus, is there a reliable cross-platform way to check whether I have reached a root in the file system?

Asked By: Philippe

||

Source

Answer 1

I don’t think you can find out if it’s a file system root portably, however I’d suggest doing a call to os.path.realpath() on both the current dir and your calculated parent and compare if they’re the same — this means you are spinning your wheels and there’s no point in proceeding.

For example:

>>> os.path.realpath('/usr/bin/..')
'/usr'
>>> os.path.realpath('/usr/bin/../..')
'/'
>>> os.path.realpath('/usr/bin/../../..')
'/'
>>> os.path.realpath('/..')
'/'

Answered By: FatalError

Answer 2

if os.path.dirname(path) == path:
    # you have yourself root.
    # works on Windows and *nix paths.
    # does NOT work on Windows shares (\servershare)

Answered By: ddotsenko

Answer 3

This works for us on Linux. Not sure about Windows, however:

def _find_root(start, stop, func=os.path.exists):
    """Search up the start hierarchy for stop; return None at the FS root.

    Uses func() to determine if stop exists; default is os.path.exists().
    """
    if func(os.path.join(start, stop)):
        return start
    else:
        if os.path.samefile(start, os.path.dirname(start)):
           return None
        else:
           return _find_root(os.path.dirname(start), stop)

We use os.path.normpath(start) in the call to this function.

Answered By: Mark E. Hamilton

Answer 4

With pathlib.Path there’s a sharp edge if one wants to do it properly. For Path("~/../../") to work, one has to use expanduser() and resolve() in correct order:

from pathlib import Path

path = Path("~/../..")
path = path.expanduser().resolve()
if path.parent == path:
    print("This points to fs root!")

Otherwise, the condition will end up with a path that is ../ away from CWD.

Answered By: Błażej Michalik

Answer 5

pathlib paths have an anchor property to do just that. So you can just check if you’re at the absolute path’s root:

from pathlib import Path

absolute_path = Path(path_to_check).absolute()
if absolute_path == Path(absolute_path.anchor):
   print("it's a root")

It’s your choice whether to use absolute or resolve, they handle symlinks differently.

Answered By: trutheality

Check if a directory is a (file system) root

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