From c4232c6dacfe15300d092c826cf5c1773b39d287 Mon Sep 17 00:00:00 2001
From: Troy Tamas <troy.tamas@rockleyphotonics.com>
Date: Wed, 23 Dec 2020 20:25:29 +0900
Subject: [PATCH] returning a copy of the cached bounding box

---
 gdspy/library.py | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/gdspy/library.py b/gdspy/library.py
index 2c7c099..1e197bd 100644
--- a/gdspy/library.py
+++ b/gdspy/library.py
@@ -578,11 +578,16 @@ def get_bounding_box(self):
                 bb[0, 1] = min(bb[0, 1], all_points[1].min())
                 bb[1, 0] = max(bb[1, 0], all_points[0].max())
                 bb[1, 1] = max(bb[1, 1], all_points[1].max())
-                self._bounding_box = numpy.asarray(bb)
+                self._bounding_box = bb
             else:
                 self._bounding_box = None
             self._bb_valid = True
-        return self._bounding_box
+
+        if self._bounding_box is None:
+            return None
+        else:
+            # return a *copy* of the cached bounding box to ensure it doesn't get inadvertently modified
+            return numpy.array(self._bounding_box)
 
     def get_polygons(self, by_spec=False, depth=None):
         """