raise dimension error

pygeoif/geometry.py

@@ -251,11 +251,9 @@ def y(self) -> float:
     @property
     def z(self) -> Optional[float]:
         """Return z coordinate."""
-        return (
-            self._coordinates[2]  # type: ignore[misc]
-            if len(self._coordinates) == 3
-            else None
-        )
+        if self.has_z:
+            return self._coordinates[2]  # type: ignore [misc]
+        raise DimensionError(f"The {self!r} geometry does not have z values")
 
     @property
     def coords(self) -> Tuple[PointType]:

tests/test_point.py

@@ -5,6 +5,7 @@
 import pytest
 
 from pygeoif import geometry
+from pygeoif.exceptions import DimensionError
 
 
 def test_empty() -> None:
@@ -52,11 +53,19 @@ def test_bounds3d() -> None:
 def test_xy() -> None:
     point = geometry.Point(1.0, 0.0)
 
-    assert point.z is None
     assert point.x == 1
     assert point.y == 0
 
 
+def test_xy_raises_error_accessing_z() -> None:
+    point = geometry.Point(1, 0)
+
+    with pytest.raises(
+        DimensionError, match=r"^The Point\(1, 0\) geometry does not have z values$"
+    ):
+        point.z
+
+
 def test_xyz() -> None:
     point = geometry.Point(1.0, 0.0, 2.0)