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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _add_file(self, path, **params):
 """ Attempt to add a file to the system monitoring mechanism. """

        log = self._getparam('log', self._discard, **params)
        fd = None
        try:
            fd = os.open(path, os.O_RDONLY)
        except Exception as e:
            if not self.paths[path]:
                log.error("Open failed on watched path %r -- %s", path, e, exc_info=log.isEnabledFor(logging.DEBUG))
                raise e
            elif path in self.paths_pending:
                log.debug("path %r is still pending -- %s", path, e)
            else:
                self.paths_pending[path] = True
                log.debug("Added %r to pending list after open failure -- %s", path, e)
            return False
        if self._mode == WF_KQUEUE:
            log.debug("path %s opened as fd %d", path, fd)
            try:
                ev = select.kevent(fd,
                    filter=select.KQ_FILTER_VNODE,
                    flags=select.KQ_EV_ADD | select.KQ_EV_CLEAR,
                    fflags=select.KQ_NOTE_WRITE | select.KQ_NOTE_ATTRIB | select.KQ_NOTE_LINK |
                                select.KQ_NOTE_DELETE | select.KQ_NOTE_RENAME)
                self._kq.control([ev], 0, 0)
            except Exception as e:
                log.error("kevent failed on watched path %r -- %s", path, e)
                try: os.close(fd)
                except: pass
                raise e

        elif self._mode == WF_INOTIFYX:
            #  inotify doesn't need the target paths open, so now it is known to be
            #  accessible, close the actual fd and use the watch-descriptor as the fd.
            #
            #  However, due to an apparent simfs bug where inotify does not fire either
            #  IN_DELETE_SELF or IN_MOVE_SELF, we need to record the inode so that we
            #  can detect deletes and renames internally.  simfs is used in containers.
            #
            try:
                s = os.fstat(fd)
                self._inx_inode[path] = s.st_ino
            except Exception as e:
                log.error("fstat(%d) failed on open path %r -- %s", fd, path, e)
                try: os.close(fd)
                except: pass
                raise e
            try: os.close(fd)
            except: pass
            try:
                fd = pynotifyx.add_watch(self._inx_fd, path, self._inx_mask)
                log.debug("path %s watched with wd %d", path, fd)
            except Exception as e:
                log.error("inotify failed on watched path %r -- %s", path, e)
                raise e

        elif self._mode == WF_POLLING:
            log.debug("path %s opened as fd %d", path, fd)
            fstate = self._poll_get_stat(fd, path)
            if fstate:
                self._poll_stat[fd] = fstate

        self.paths_open[path] = fd
        self.fds_open[fd] = path
        return True