Added bounding box method for Polygon object.

.gitignore

@@ -2,6 +2,7 @@ MANIFEST
 *.gds
 docs/_*
 .*.swp
+.DS_Store
 
 # Byte-compiled / optimized / DLL files
 __pycache__/

gdspy/__init__.py

@@ -173,13 +173,33 @@ def __init__(self, points, layer=0, datatype=0, verbose=True):
                 RuntimeWarning,
                 stacklevel=2)
         self.layer = layer
+
+        if isinstance(points[0][0], list):
+            raise ValueError('points cannot be a 3D array')
+
         self.points = numpy.array(points)
         self.datatype = datatype
 
     def __str__(self):
         return "Polygon ({} vertices, layer {}, datatype {})".format(
             len(self.points), self.layer, self.datatype)
 
+    def get_bounding_box(self):
+        """
+        Returns the bounding box of the polygon.
+
+        Returns
+        -------
+        out : Numpy array[2,2] or ``None``
+            Bounding box of this polygon [[x_min, y_min], [x_max, y_max]], or
+            ``None`` if the polygon is empty.
+        """
+        if len(self.points) == 0:
+            return None
+
+        return numpy.array(((self.points[:, 0].min(), self.points[:, 1].min()), 
+                            (self.points[:, 0].max(), self.points[:, 1].max())))
+
     def to_gds(self, multiplier):
         """
         Convert this object to a GDSII element.