I wonder why in filesystems.AbstractedFS.chdir use os.chdir

[mike96265]

` class AbstractedFS:

def chdir(self, path):

    """Change the current directory. If this method is overridden
    it is vital that `cwd` attribute gets set.
    """

    # note: process cwd will be reset by the caller

    assert isinstance(path, unicode), path

    os.chdir(path)

    self.cwd = self.fs2ftp(path)

` why AbstractFS.chdir going to use os.chdir here,It seems no effect.

and after I remove this line,this program works fine.