Tentative: fix for ParamSpec on Python < 3.10

Alternate solution is to remove the callable typing on CallAfter and CallLater

etgtools/pi_generator.py

@@ -84,6 +84,10 @@ from enum import IntEnum, IntFlag, auto
 from typing import (Any, overload, TypeAlias, TypeVar, ParamSpec, Generic,
     Union, Optional, List, Tuple, Callable
 )
+try:
+    from typing import ParamSpec
+except ImportError:
+    from typing_extensions import ParamSpec
 
 """
 

requirements/devel.txt

@@ -22,3 +22,4 @@ markupsafe==1.1.1
 doc2dash==2.3.0
 beautifulsoup4
 attrdict3 ; sys_platform == 'win32'
+typing-extensions; python_version < '3.10'

requirements/install.txt

@@ -3,3 +3,4 @@ numpy < 1.17 ; python_version <= '2.7'
 numpy ; python_version >= '3.0' and python_version < '3.12'
 # pillow < 3.0
 six
+typing-extensions; python_version < '3.10'