pylint of dipole

Addresses BruceSherwood#76

site-packages/visual/examples/dipole.py

@@ -1,41 +1,48 @@
-from visual import *
-
-print("""
+#!/usr/bin/env python
+#coding:utf-8
+"""
 Click to plot a normalized electric field vector.
 Vectors are blue if low magnitude, red if high.
 Right button drag or Ctrl-drag to rotate camera to view scene.
 
 Middle button drag or Alt-drag to zoom in or out.
   On a two-button mouse, middle is left + right.
-""")
+"""
+from __future__ import print_function, division
+
+#from visual import *
+import visual as vp
+print(__doc__)
 
-ec = 1.6e-19  # electron charge
+EC = 1.6e-19  # electron charge
 
-scene.title="Electric Field Vectors"
-scene.range = 2e-13
+vp.scene.title = "Electric Field Vectors"
+vp.scene.range = 2e-13
 
-charges = [ sphere( pos = (-1e-13,0,0), Q =  ec, color=color.red, radius = 6e-15 ),
-            sphere( pos = ( 1e-13,0,0), Q = -ec, color=color.blue, radius = 6e-15 ),
-          ]
+CHARGES = [
+    vp.sphere(pos=(-1e-13, 0, 0), Q=EC, color=vp.color.red, radius=6e-15),
+    vp.sphere(pos=(1e-13, 0, 0), Q=-EC, color=vp.color.blue, radius=6e-15),
+]
 
-def getfield(p):
-    f = vector(0,0,0)
-    for c in charges:
-        f = f + (p-c.pos) * 8.988e9 * c.Q / mag(p-c.pos)**3
-    return f
+def getfield(posn):
+    """ Get the field at a given point."""
+    fld = vp.vector(0, 0, 0)
+    for chrg in CHARGES:
+        fld = fld + (posn-chrg.pos) * 8.988e9 * chrg.Q / vp.mag(posn-chrg.pos)**3
+    return fld
 
 while True:
-    p = scene.mouse.getclick().pos
-    f = getfield(p)
-    m = mag(f)
-    red = maximum( 1-1e17/m, 0 )
-    blue = minimum(   1e17/m, 1 )
-    if red >= blue:
-        blue = blue/red
-        red = 1.0
+    POSN = vp.scene.mouse.getclick().pos
+    FLD = getfield(POSN)
+    MAG = vp.mag(FLD)
+    RED = vp.maximum(1-1e17/MAG, 0)
+    BLUE = vp.minimum(1e17/MAG, 1)
+    if RED >= BLUE:
+        BLUE = BLUE/RED
+        RED = 1.0
     else:
-        red = red/blue
-        blue = 1.0
-    arrow( pos=p, axis=f * (4e-14/1e17),
-           shaftwidth = 6e-15,
-           color=(red,0,blue))
+        RED = RED/BLUE
+        BLUE = 1.0
+    vp.arrow(pos=POSN, axis=FLD * (4e-14/1e17),
+             shaftwidth=6e-15,
+             color=(RED, 0, BLUE))