python version agnostic method to get package files

trackhub/trackhub_from_excel

@@ -1,5 +1,7 @@
 #!/usr/bin/env python
 
+import sys
+import os
 import importlib.resources
 import trackhub
 from collections import defaultdict
@@ -585,10 +587,13 @@ def create_example(filename):
     This uses the example file that is shipped with the trackhub package, and
     adds two new sheets to include absolute paths to the example data.
     """
-    # Find the package's data directory
-    data = importlib.resources.files("trackhub") / "test" / "data"
-
-    wb = load_workbook(data / "example.xlsx", data_only=True)
+    # In Python >=3.9, importlib.resources.files would work, but the method
+    # used here is agnostic to Python versions.
+    example_file = os.path.join(
+        os.path.dirname(sys.modules['trackhub'].__file),
+        "example.xlsx"
+    )
+    wb = load_workbook(example_file, data_only=True)
 
     bigbeds = wb.create_sheet("bigbeds")
     bigbeds.append(