def parent_dir(path):
    """same as os.path.dirname but returns '.' instead of ''
    for paths that just have a filename in it e.g. 'foo'"""
    pdir = os.path.dirname(path)
    if pdir == '':
        pdir = '.'
    return pdir


def copy_ownership(dst, src):
    """copy user and group ownership from own_src file/dir to dst file/dir.
    If own_src is None, the containing directory is used as source."""
    if os.name != 'posix':
        return False
    try:
        s = os.stat(src)
        os.chown(dst, s.st_uid, s.st_gid)
    except OSError, e:
        warning("IOError: %s" % (e,))
        warning("Unable to copy ownership from '%s' to '%s'" % (src, dst))
    return True


def mkdir(path, ownership_src=None):
    """creates the directory 'path'. If ownership_src is given, copies (chown)
    usr/grp ownership from 'ownership_src' to 'path'"""
    os.mkdir(path)
    if ownership_src != None:
        copy_ownership(path, ownership_src)