How to use the dulwich.file.GitFile function in dulwich

def move_in_pack(self, path):
        """Move a specific file containing a pack into the pack directory.

        :note: The file should be on the same file system as the
            packs directory.

        :param path: Path to the pack file.
        """
        with PackData(path) as p:
            entries = p.sorted_entries()
            basename = self._get_pack_basepath(entries)
            with GitFile(basename+".idx", "wb") as f:
                write_pack_index_v2(f, entries, p.get_stored_checksum())
        os.rename(path, basename + ".pack")
        final_pack = Pack(basename)
        self._add_known_pack(basename, final_pack)
        return final_pack

def keep(self, msg=None):
        """Add a .keep file for the pack, preventing git from garbage collecting it.

        :param msg: A message written inside the .keep file; can be used later
            to determine whether or not a .keep file is obsolete.
        :return: The path of the .keep file, as a string.
        """
        keepfile_name = '%s.keep' % self._basename
        with GitFile(keepfile_name, 'wb') as keepfile:
            if msg:
                keepfile.write(msg)
                keepfile.write(b'\n')
        return keepfile_name

def remove_if_equals(self, name, old_ref):
        """Remove a refname only if it currently equals old_ref.

        This method does not follow symbolic references. It can be used to
        perform an atomic compare-and-delete operation.

        :param name: The refname to delete.
        :param old_ref: The old sha the refname must refer to, or None to
            delete unconditionally.
        :return: True if the delete was successful, False otherwise.
        """
        self._check_refname(name)
        filename = self.refpath(name)
        ensure_dir_exists(os.path.dirname(filename))
        f = GitFile(filename, 'wb')
        try:
            if old_ref is not None:
                orig_ref = self.read_loose_ref(name)
                if orig_ref is None:
                    orig_ref = self.get_packed_refs().get(name, ZERO_SHA)
                if orig_ref != old_ref:
                    return False
            # may only be packed
            try:
                os.remove(filename)
            except OSError as e:
                if e.errno != errno.ENOENT:
                    raise
            self._remove_packed_ref(name)
        finally:
            # never write, we just wanted the lock

def read(self):
        """Read current contents of index from disk."""
        if not os.path.exists(self._filename):
            return
        f = GitFile(self._filename, 'rb')
        try:
            f = SHA1Reader(f)
            for x in read_index(f):
                self[x[0]] = IndexEntry(*x[1:])
            # FIXME: Additional data?
            f.read(os.path.getsize(self._filename)-f.tell()-20)
            f.check_sha()
        finally:
            f.close()

def move_in_pack(self, path):
        """Move a specific file containing a pack into the pack directory.

        Note: The file should be on the same file system as the
            packs directory.

        Args:
          path: Path to the pack file.
        """
        with PackData(path) as p:
            entries = p.sorted_entries()
            basename = self._get_pack_basepath(entries)
            index_name = basename + ".idx"
            if not os.path.exists(index_name):
                with GitFile(index_name, "wb") as f:
                    write_pack_index_v2(f, entries, p.get_stored_checksum())
        for pack in self.packs:
            if pack._basename == basename:
                return pack
        target_pack = basename + '.pack'
        if sys.platform == 'win32':
            # Windows might have the target pack file lingering. Attempt
            # removal, silently passing if the target does not exist.
            try:
                os.remove(target_pack)
            except (IOError, OSError) as e:
                if e.errno != errno.ENOENT:
                    raise
        os.rename(path, target_pack)
        final_pack = Pack(basename)
        self._add_cached_pack(basename, final_pack)

def get_description(self):
        """Retrieve the description of this repository.

        :return: A string describing the repository or None.
        """
        path = os.path.join(self._controldir, 'description')
        try:
            with GitFile(path, 'rb') as f:
                return f.read()
        except (IOError, OSError) as e:
            if e.errno != errno.ENOENT:
                raise
            return None

def write_to_path(self, path=None):
        """Write configuration to a file on disk."""
        if path is None:
            path = self.path
        with GitFile(path, 'wb') as f:
            self.write_to_file(f)

def _put_named_file(self, path, contents):
        """Write a file to the control dir with the given name and contents.

        :param path: The path to the file, relative to the control dir.
        :param contents: A string to write to the file.
        """
        path = path.lstrip(os.path.sep)
        with GitFile(os.path.join(self.controldir(), path), 'wb') as f:
            f.write(contents)

"""Remove a refname only if it currently equals old_ref.

        This method does not follow symbolic references. It can be used to
        perform an atomic compare-and-delete operation.

        Args:
          name: The refname to delete.
          old_ref: The old sha the refname must refer to, or None to
            delete unconditionally.
          message: Optional message
        Returns: True if the delete was successful, False otherwise.
        """
        self._check_refname(name)
        filename = self.refpath(name)
        ensure_dir_exists(os.path.dirname(filename))
        f = GitFile(filename, 'wb')
        try:
            if old_ref is not None:
                orig_ref = self.read_loose_ref(name)
                if orig_ref is None:
                    orig_ref = self.get_packed_refs().get(name, ZERO_SHA)
                if orig_ref != old_ref:
                    return False

            # remove the reference file itself
            try:
                os.remove(filename)
            except OSError as e:
                if e.errno != errno.ENOENT:  # may only be packed
                    raise

            self._remove_packed_ref(name)