From 4d30ae540d6d6e49cc3bbb74bd5826c98f196456 Mon Sep 17 00:00:00 2001
From: Robert McArthur <robert.mcarthur@anu.edu.au>
Date: Wed, 1 May 2024 16:57:33 +1000
Subject: [PATCH] DEV: resolve import error on 3.9

---
 src/cogent3/app/typing.py | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/cogent3/app/typing.py b/src/cogent3/app/typing.py
index 7836e83f5..803e5ff0f 100644
--- a/src/cogent3/app/typing.py
+++ b/src/cogent3/app/typing.py
@@ -4,13 +4,20 @@
 
 import inspect
 import re
+import sys
 
 from typing import ForwardRef, TypeVar, Union
-from types import UnionType
 
 from typing_extensions import get_args, get_origin
 
 
+if sys.version_info.minor >= 10:
+    from types import UnionType
+
+    NESTED_HINTS = (Union, UnionType, list, tuple, set)
+else:
+    NESTED_HINTS = (Union, list, tuple, set)
+
 AlignedSeqsType = TypeVar("AlignedSeqsType", "Alignment", "ArrayAlignment")
 UnalignedSeqsType = TypeVar("UnalignedSeqsType", bound="SequenceCollection")
 SeqsCollectionType = Union[AlignedSeqsType, UnalignedSeqsType]
@@ -76,7 +83,7 @@ def get_constraint_names(*hints) -> set[str | type]:
             all_hints.update(hint.__constraints__)
             continue
 
-        if get_origin(hint) in (Union, UnionType, list, tuple, set):
+        if get_origin(hint) in NESTED_HINTS:
             all_hints.update(get_constraint_names(*get_args(hint)))
 
         if type(hint) == type: