The following patch should fix the problem.
renzo
----
diff -Naur grip-4.2.0/debian/control grip-4.2.0.fixed/debian/control
--- grip-4.2.0/debian/control 2016-07-03 23:21:52.000000000 +0200
+++ grip-4.2.0.fixed/debian/control 2023-09-13 15:20:13.527645376 +0200
@@ -12,6 +12,7 @@
python3-requests,
python3-responses (>= 0.5.0),
python3-setuptools
+ python3-werkzeug
Build-Depends-Indep: txt2man
Standards-Version: 3.9.8
Testsuite: autopkgtest
diff -Naur grip-4.2.0/grip/assets.py grip-4.2.0.fixed/grip/assets.py
--- grip-4.2.0/grip/assets.py 2016-04-16 17:51:39.000000000 +0200
+++ grip-4.2.0.fixed/grip/assets.py 2023-09-13 15:20:59.344112922 +0200
@@ -13,7 +13,7 @@
from urllib.parse import urljoin
import requests
-from flask import safe_join
+from werkzeug.utils import safe_join
from .constants import (
STYLE_URLS_SOURCE, STYLE_URLS_RE, STYLE_ASSET_URLS_RE,
diff -Naur grip-4.2.0/grip/readers.py grip-4.2.0.fixed/grip/readers.py
--- grip-4.2.0/grip/readers.py 2016-04-16 17:51:39.000000000 +0200
+++ grip-4.2.0.fixed/grip/readers.py 2023-09-13 15:21:13.596250094 +0200
@@ -8,7 +8,7 @@
import sys
from abc import ABCMeta, abstractmethod
-from flask import safe_join
+from werkzeug.utils import safe_join
from .constants import DEFAULT_FILENAMES, DEFAULT_FILENAME
from .exceptions import ReadmeNotFoundError
