From 3623408bc54baad55d8429a178dd408fc89e1115 Mon Sep 17 00:00:00 2001
From: Jonathan Shimwell <mail@jshimwell.com>
Date: Thu, 27 Oct 2022 17:38:27 +0100
Subject: [PATCH] avoid namespace overwrite of union

---
 openmc/checkvalue.py      | 4 ++--
 openmc/deplete/results.py | 7 ++++---
 openmc/material.py        | 4 ++--
 openmc/settings.py        | 9 +++++----
 openmc/source.py          | 1 +
 5 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/openmc/checkvalue.py b/openmc/checkvalue.py
index c5d80b2fcb..840306486f 100644
--- a/openmc/checkvalue.py
+++ b/openmc/checkvalue.py
@@ -1,12 +1,12 @@
 import copy
 import os
-from typing import Union
+import typing  # required to prevent typing.Union namespace overwriting Union
 from collections.abc import Iterable
 
 import numpy as np
 
 # Type for arguments that accept file paths
-PathLike = Union[str, os.PathLike]
+PathLike = typing.Union[str, os.PathLike]
 
 
 def check_type(name, value, expected_type, expected_iter_type=None, *, none_ok=False):
diff --git a/openmc/deplete/results.py b/openmc/deplete/results.py
index d9aa52b79e..9552a6ba61 100644
--- a/openmc/deplete/results.py
+++ b/openmc/deplete/results.py
@@ -1,7 +1,8 @@
 import numbers
 import bisect
 import math
-from typing import Iterable, Optional, Tuple, Union
+import typing  # required to prevent typing.Union namespace overwriting Union
+from typing import Iterable, Optional, Tuple
 from warnings import warn
 
 import h5py
@@ -95,7 +96,7 @@ class Results(list):
 
     def get_atoms(
         self,
-        mat: Union[Material, str],
+        mat: typing.Union[Material, str],
         nuc: str,
         nuc_units: str = "atoms",
         time_units: str = "s"
@@ -165,7 +166,7 @@ class Results(list):
 
     def get_reaction_rate(
         self,
-        mat: Union[Material, str],
+        mat: typing.Union[Material, str],
         nuc: str,
         rx: str
     ) -> Tuple[np.ndarray, np.ndarray]:
diff --git a/openmc/material.py b/openmc/material.py
index 1979b39588..10ade8bfe4 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -6,7 +6,7 @@ from pathlib import Path
 import re
 import typing  # imported separately as py3.8 requires typing.Iterable
 import warnings
-from typing import Optional, Union
+from typing import Optional
 from xml.etree import ElementTree as ET
 
 import h5py
@@ -968,7 +968,7 @@ class Material(IDManagerMixin):
 
         Returns
         -------
-        Union[dict, float]
+        typing.Union[dict, float]
             If by_nuclide is True then a dictionary whose keys are nuclide
             names and values are activity is returned. Otherwise the activity
             of the material is returned as a float.
diff --git a/openmc/settings.py b/openmc/settings.py
index ad5a9b28ae..45658f8127 100644
--- a/openmc/settings.py
+++ b/openmc/settings.py
@@ -6,7 +6,8 @@ import itertools
 from math import ceil
 from numbers import Integral, Real
 from pathlib import Path
-from typing import Optional, Union
+import typing  # required to prevent typing.Union namespace overwriting Union
+from typing import Optional
 from xml.etree import ElementTree as ET
 
 import openmc.checkvalue as cv
@@ -582,7 +583,7 @@ class Settings:
         self._max_order = max_order
 
     @source.setter
-    def source(self, source: Union[Source, typing.Iterable[Source]]):
+    def source(self, source: typing.Union[Source, typing.Iterable[Source]]):
         if not isinstance(source, MutableSequence):
             source = [source]
         self._source = cv.CheckedList(Source, 'source distributions', source)
@@ -843,7 +844,7 @@ class Settings:
 
     @volume_calculations.setter
     def volume_calculations(
-        self, vol_calcs: Union[VolumeCalculation, typing.Iterable[VolumeCalculation]]
+        self, vol_calcs: typing.Union[VolumeCalculation, typing.Iterable[VolumeCalculation]]
     ):
         if not isinstance(vol_calcs, MutableSequence):
             vol_calcs = [vol_calcs]
@@ -889,7 +890,7 @@ class Settings:
         self._write_initial_source = value
 
     @weight_windows.setter
-    def weight_windows(self, value: Union[WeightWindows, typing.Iterable[WeightWindows]]):
+    def weight_windows(self, value: typing.Union[WeightWindows, typing.Iterable[WeightWindows]]):
         if not isinstance(value, MutableSequence):
             value = [value]
         self._weight_windows = cv.CheckedList(WeightWindows, 'weight windows', value)
diff --git a/openmc/source.py b/openmc/source.py
index a5907344e7..d886e98910 100644
--- a/openmc/source.py
+++ b/openmc/source.py
@@ -3,6 +3,7 @@ from enum import Enum
 from numbers import Real
 import warnings
 import typing  # imported separately as py3.8 requires typing.Iterable
+# also required to prevent typing.Union namespace overwriting Union
 from typing import Optional
 from xml.etree import ElementTree as ET