Corrected faulty import of PI.

src/multitouch/touch.py

 #!/usr/bin/env python
 from events import TapEvent, FlickEvent, RotateEvent, PinchEvent, PanEvent
 import time
-from math import atan2, PI
+from math import atan2, pi
 from threading import Thread
 from OSC import OSCServer
 
@@ -137,11 +137,11 @@ class MultiTouchListener(object):
             p.set_angle(atan2(p.y - cy, p.x - cx))
             da = p.angle_diff()
 
-            # Assert that angle is in [-PI, PI]
-            if da > PI:
-                da -= 2 * PI
-            elif da < PI:
-                da += 2 * PI
+            # Assert that angle is in [-pi, pi]
+            if da > pi:
+                da -= 2 * pi
+            elif da < pi:
+                da += 2 * pi
 
             rotation += da