diff --git a/src/amuse/datamodel/rotation.py b/src/amuse/datamodel/rotation.py
index 4235ae6c99..69bb1cf2b8 100644
--- a/src/amuse/datamodel/rotation.py
+++ b/src/amuse/datamodel/rotation.py
@@ -1,40 +1,53 @@
 import numpy
 from amuse.units.trigo import cos, sin
 
+
 def new_rotation_matrix(phi, theta, psi):
     """
-    Return the rotation matrix, to rotate positions, around the x-axis (phi), y-axis (theta) and z-axis (psi).
-    See wikipedia for reference
+    Returns the rotation matrix, to rotate positions, around the x-axis (phi),
+    y-axis (theta) and z-axis (psi).  See wikipedia for reference
     """
-    
-    return numpy.array( (
-        (cos(theta)*cos(psi), -cos(phi)*sin(psi) + sin(phi)*sin(theta)*cos(psi),  sin(phi)*sin(psi) + cos(phi)*sin(theta)*cos(psi)) ,
-        (cos(theta)*sin(psi),  cos(phi)*cos(psi) + sin(phi)*sin(theta)*sin(psi), -sin(phi)*cos(psi) + cos(phi)*sin(theta)*sin(psi)) ,
-        (-sin(theta)        ,  sin(phi)*cos(theta)                             ,  cos(phi)*cos(theta))
-    ) )
+
+    return numpy.array(
+        (
+            (
+                cos(theta) * cos(psi),
+                -cos(phi) * sin(psi) + sin(phi) * sin(theta) * cos(psi),
+                sin(phi) * sin(psi) + cos(phi) * sin(theta) * cos(psi),
+            ),
+            (
+                cos(theta) * sin(psi),
+                cos(phi) * cos(psi) + sin(phi) * sin(theta) * sin(psi),
+                -sin(phi) * cos(psi) + cos(phi) * sin(theta) * sin(psi),
+            ),
+            (-sin(theta), sin(phi) * cos(theta), cos(phi) * cos(theta)),
+        )
+    )
+
 
 def rotated(positions, phi, theta, psi):
     """
     Return the positions, rotated by phi, theta and psi around the x, y and z axes
     """
-#    print phi, theta, psi
+    #    print phi, theta, psi
     rotation_matrix = new_rotation_matrix(phi, theta, psi)
-#    print "RT=", rotation_matrix
+    #    print "RT=", rotation_matrix
     return positions.dot(rotation_matrix.transpose())
 
+
 def rotate(particles, phi, theta, psi):
     """
     Rotate the positions and the velocities around 0,0,0.
     """
-    particles.position = rotated(particles.position,  phi, theta, psi)
-    particles.velocity = rotated(particles.velocity,  phi, theta, psi)
+    particles.position = rotated(particles.position, phi, theta, psi)
+    particles.velocity = rotated(particles.velocity, phi, theta, psi)
+
 
 def add_spin(particles, omega):
     """
-    Add solid-body rotation to the velocity of the particles, relative to the 
+    Add solid-body rotation to the velocity of the particles, relative to the
     center-of-mass position.
     """
     if not omega.is_vector():
         omega = omega * [0.0, 0.0, 1.0]
     particles.velocity += omega.cross(particles.position - particles.center_of_mass())
-