Update flask version in requirements.txt, use escape from markupsafe package.

app/account_service.py

@@ -1,4 +1,5 @@
 from flask import *
+from markupsafe import escape
 from Login import check_username_availability, verify_user, add_user, get_expiry_date, change_password, WarningMessage
 
 

app/admin_service.py

@@ -1,5 +1,6 @@
 # System Library
 from flask import *
+from markupsafe import escape
 
 # Personal library
 from Yaml import yml

app/main.py

@@ -5,7 +5,8 @@
 # Copyright 2019 (C) Hui Lan <hui.lan@cantab.net>
 # Written permission must be obtained from the author for commercial uses.
 ###########################################################################
-from flask import escape, abort
+from flask import abort
+from markupsafe import escape
 from Login import *
 from Article import *
 import Yaml

requirements.txt

@@ -1,4 +1,4 @@
-Flask==1.1.2
+Flask==2.3.2
 selenium==3.141.0
 PyYAML~=6.0
 pony==0.7.16