🎨 use python3 syntax

add othre version working with python2

source/_static/code/vol_of_sphere.py

@@ -3,6 +3,17 @@ import math
 def vol_of_sphere(radius):
     """
     compute the volume of sphere of a given radius
+    work only in python3
+    """
+    
+    vol = 4 / 3 * math.pi * pow(radius, 3)
+    return vol
+
+
+def vol_of_sphere_python2(radius):
+    """
+    compute the volume of sphere of a given radius
+    work with python2 and 3
     """
 
     vol = float(4) / float(3) * float(math.pi) * pow(radius, 3)