fix: use postponed evaluation

* 6899ae1 switched list[... to List[... for compat with python 3.8
* instead opt into postponed evaluation per suggestion
* drop CI tests from python 3.9 to 3.8

.github/workflows/ex-workflow.yml

@@ -39,7 +39,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v4
         with:
-          python-version: 3.9
+          python-version: 3.8
 
       - name: Print python version
         run: |
@@ -118,7 +118,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v4
         with:
-          python-version: 3.9
+          python-version: 3.8
 
       - name: Install Python packages
         run: |

common/DisvGridMerger.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from math import sqrt
 import copy
 

common/DisvPropertyContainer.py

@@ -1,6 +1,7 @@
+from __future__ import annotations
+
 import copy
 from itertools import cycle
-from typing import List
 
 import matplotlib.pyplot as plt
 import numpy as np
@@ -104,10 +105,10 @@ class DisvPropertyContainer:
     nlay: int
     ncpl: int
     nvert: int
-    vertices: List[list]  # [[iv, xv, yv], ...]
-    cell2d: List[list]  # [[ic, xc, yc, ncvert, icvert], ...]
+    vertices: list[list]  # [[iv, xv, yv], ...]
+    cell2d: list[list]  # [[ic, xc, yc, ncvert, icvert], ...]
     top: np.ndarray
-    botm: List[np.ndarray]
+    botm: list[np.ndarray]
     origin_x: float
     origin_y: float
     rotation: float
@@ -541,7 +542,7 @@ def plot_grid(
             plot_time = -1.0
 
         if not isinstance(grid_color, tuple):
-            grid_color = (grid_color, )
+            grid_color = (grid_color,)
 
         ColorCycler = grid_color
         if plot_time > 0.0 and grid_color == ("grey",):