Make scipy optional again and declare packaging

pyproject.toml

@@ -30,6 +30,7 @@ classifiers = [
 requires-python = ">=3.8"
 dependencies = [
     "numpy>=1.0",
+    "packaging",
     "spglib>=1.14.1",
 ]
 license = {text = "The MIT license"}

seekpath/brillouinzone/brillouinzone.py

@@ -1,11 +1,15 @@
 """Module to compute the Brillouin zone of a crystal."""
 
+from __future__ import annotations
+
 from collections import defaultdict
 import warnings
-from typing import Union
+from typing import TYPE_CHECKING, Union
 
 import numpy as np
-from scipy.spatial import Voronoi, ConvexHull, Delaunay
+
+if TYPE_CHECKING:
+    from scipy.spatial import ConvexHull, Delaunay
 
 
 def get_BZ(
@@ -127,6 +131,9 @@ def _initialize_BZ(
             plotting library prefers these - these are not oriented for the
             time being)
         """
+        # scipy is the optional `bz` extra, so import it only when a BZ is built.
+        from scipy.spatial import ConvexHull, Delaunay, Voronoi
+
         ret_data = {}
 
         supercell_size = 3  # Is this enough?

tests/test_import_without_scipy.py

@@ -0,0 +1,10 @@
+"""scipy is only needed for the Brillouin zone (the `bz` extra)."""
+
+import subprocess
+import sys
+
+
+def test_import_without_scipy():
+    """`import seekpath` must work when scipy is not installed."""
+    code = "import sys; sys.modules['scipy'] = None; import seekpath"
+    subprocess.run([sys.executable, '-c', code], check=True)