diff --git a/src/animate.py b/src/animate.py
index 4ef081a..67b88ea 100644
--- a/src/animate.py
+++ b/src/animate.py
@@ -10,8 +10,8 @@
 
 # Imports and external programs
 
-from __future__ import absolute_import
-import sys, os, subprocess, re, glob
+from __future__ import print_function, absolute_import
+import sys, os, re, glob
 try:
   from Tkinter import *
 except ImportError:
diff --git a/src/bdump.py b/src/bdump.py
index 8032f58..ac75c04 100644
--- a/src/bdump.py
+++ b/src/bdump.py
@@ -11,7 +11,7 @@
 # Imports and external programs
 
 from __future__ import print_function, absolute_import
-import sys, subprocess, re, glob, types
+import sys, re, glob, types
 import functools
 from os import popen
 
diff --git a/src/dump.py b/src/dump.py
index 1f1ac25..6d6280b 100644
--- a/src/dump.py
+++ b/src/dump.py
@@ -11,7 +11,7 @@
 # Imports and external programs
 
 from __future__ import print_function, absolute_import
-import sys, subprocess, re, glob, types
+import sys, re, glob, types
 from os import popen
 from math import *             # any function could be used by set()
 import os
diff --git a/src/dump2force.py b/src/dump2force.py
index 6e71ea9..1df3ffb 100644
--- a/src/dump2force.py
+++ b/src/dump2force.py
@@ -27,7 +27,7 @@ and dump match the format here - this will be checked in future!
 
 """
 
-from __future__ import absolute_import
+from __future__ import print_function, absolute_import
 from evtk.vtk import VtkFile, VtkGroup, VtkUnstructuredGrid
 from bdump import bdump
 import numpy as np
diff --git a/src/gl.py b/src/gl.py
index 28057b6..7f99d34 100644
--- a/src/gl.py
+++ b/src/gl.py
@@ -10,7 +10,7 @@
 
 # Imports and external programs
 
-from __future__ import absolute_import
+from __future__ import print_function, absolute_import
 
 from math import sin,cos,sqrt,pi,acos
 from OpenGL.Tk import *
diff --git a/src/image.py b/src/image.py
index d664f1f..a5b42e3 100644
--- a/src/image.py
+++ b/src/image.py
@@ -11,7 +11,11 @@
 # Imports and external programs
 
 from __future__ import print_function, absolute_import
-import sys, os, subprocess, re, glob
+import sys, os, re, glob
+try:
+  import commands
+except ImportError:
+  import subprocess as commands
 from math import *
 try:
   from Tkinter import *
@@ -138,7 +142,7 @@ class image:
   def convert(self,file1,file2,switch=""):
     if file1.find('*') < 0 or file2.find('*') < 0:
       cmd = "%s %s %s %s" % (PIZZA_CONVERT,switch,file1,file2)
-      subprocess.getoutput(cmd)
+      commands.getoutput(cmd)
       return
 
     index = file1.index('*')
@@ -156,7 +160,7 @@ class image:
       cmd = "%s %s %s %s" % (PIZZA_CONVERT,switch,file1,file2)
       print(middle, end=' ')
       sys.stdout.flush()
-      subprocess.getoutput(cmd)
+      commands.getoutput(cmd)
     print()
 
   # --------------------------------------------------------------------
@@ -170,7 +174,7 @@ class image:
       if fileargs[i].find('*') < 0:
         cmd = "%s %s" % (PIZZA_MONTAGE,switch)
         for j in range(nsets): cmd += " %s" % fileargs[j]
-        subprocess.getoutput(cmd)
+        commands.getoutput(cmd)
         return
 
     nfiles = len(glob.glob(fileargs[0]))
@@ -194,7 +198,7 @@ class image:
       middle = re.search(expr,filesets[0][i]).group(1)
       fileN = "%s%s%s" % (preN,middle,postN)
       cmd += " %s" % fileN
-      subprocess.getoutput(cmd)
+      commands.getoutput(cmd)
       print(middle, end=' ')
       sys.stdout.flush()
     print()
diff --git a/src/ldump.py b/src/ldump.py
index da5b559..8660afe 100644
--- a/src/ldump.py
+++ b/src/ldump.py
@@ -11,7 +11,7 @@
 # Imports and external programs
 
 from __future__ import print_function, absolute_import
-import sys, subprocess, re, glob, types
+import sys, re, glob, types
 import functools
 from os import popen
 
diff --git a/src/mdump.py b/src/mdump.py
index 5a132fe..714add5 100644
--- a/src/mdump.py
+++ b/src/mdump.py
@@ -11,7 +11,7 @@
 # Imports and external programs
 
 from __future__ import print_function, absolute_import
-import sys, subprocess, re, glob, types
+import sys, re, glob, types
 import functools
 from os import popen
 from math import *             # any function could be used by set()
diff --git a/src/pair.py b/src/pair.py
index c1e3ce3..758f11c 100644
--- a/src/pair.py
+++ b/src/pair.py
@@ -10,7 +10,7 @@
 
 # Imports and external programs
 
-from __future__ import absolute_import
+from __future__ import print_function, absolute_import
 from math import sqrt
 
 oneline = "Compute LAMMPS pairwise energies"
diff --git a/src/patch.py b/src/patch.py
index 8651b5e..71c08fc 100644
--- a/src/patch.py
+++ b/src/patch.py
@@ -10,7 +10,7 @@
 
 # Imports and external programs
 
-from __future__ import absolute_import
+from __future__ import print_function, absolute_import
 from math import sqrt,pi,cos,sin
 from data import data
 
diff --git a/src/pizza.py b/src/pizza.py
index 7831646..cc06a53 100755
--- a/src/pizza.py
+++ b/src/pizza.py
@@ -18,7 +18,7 @@
 # modules needed by pizza.py
 
 from __future__ import print_function, absolute_import
-import sys, subprocess, os, string, glob, re
+import sys, os, string, glob, re
 import time
 
 # Help strings:
@@ -70,11 +70,13 @@ except ImportError as exception:
 
 nodisplay = False
 try:
+  import Tkinter
+  tkroot = Tkinter.Tk()
+  tkroot.withdraw()
+except ImportError as exception:
   import tkinter
   tkroot = tkinter.Tk()
   tkroot.withdraw()
-except ImportError as exception:
-  nodisplay = True
   pass
 except Exception as exception:
   nodisplay = True
diff --git a/src/plotview.py b/src/plotview.py
index b350365..e36fba8 100644
--- a/src/plotview.py
+++ b/src/plotview.py
@@ -10,7 +10,7 @@
 
 # Imports and external programs
 
-from __future__ import absolute_import
+from __future__ import print_function, absolute_import
 import sys, re, glob, time
 try:
   from Tkinter import *
diff --git a/src/rasmol.py b/src/rasmol.py
index e440046..f7838f5 100644
--- a/src/rasmol.py
+++ b/src/rasmol.py
@@ -11,7 +11,11 @@
 # Imports and external programs
 
 from __future__ import print_function, absolute_import
-import sys, os, subprocess, re, types
+import sys, os, re, types
+try:
+  import commands
+except ImportError:
+  import subprocess as commands
 from pdbfile import pdbfile
 
 oneline = "3d visualization via RasMol program"
@@ -120,7 +124,7 @@ class rasmol:
     # display the image
 
     cmd = "%s tmp.gif" % (PIZZA_DISPLAY)
-    subprocess.getoutput(cmd)
+    commands.getoutput(cmd)
 
   # --------------------------------------------------------------------
 
@@ -192,8 +196,8 @@ class rasmol:
 
     # clean up
 
-    subprocess.getoutput("rm tmp*.pdb")
-    subprocess.getoutput("rm tmp*.rasmol")
+    commands.getoutput("rm tmp*.pdb")
+    commands.getoutput("rm tmp*.rasmol")
 
   # --------------------------------------------------------------------
 
diff --git a/src/raster.py b/src/raster.py
index d67cbbf..4fc9d3b 100644
--- a/src/raster.py
+++ b/src/raster.py
@@ -11,7 +11,11 @@
 # Imports and external programs
 
 from __future__ import print_function, absolute_import
-import sys, os, subprocess, re
+import sys, os, re
+try:
+  import commands
+except ImportError:
+  import subprocess as commands
 from vizinfo import vizinfo
 from math import fabs,atan,cos,sin
 
@@ -233,7 +237,7 @@ class raster:
 
     self.single(0,self.file,box,atoms,bonds,tris,lines)
     cmd = "%s %s.png" % (PIZZA_DISPLAY,self.file)
-    subprocess.getoutput(cmd)
+    commands.getoutput(cmd)
 
   # --------------------------------------------------------------------
 
@@ -443,7 +447,7 @@ class raster:
     else:
       cmd = "cat tmp.r3d | %s -png %s.png" % (PIZZA_LABEL3D,file)
 
-    output = subprocess.getoutput(cmd)
+    output = commands.getoutput(cmd)
     return output
 
   # --------------------------------------------------------------------
diff --git a/src/svg.py b/src/svg.py
index 6ddf3f9..ca0f093 100644
--- a/src/svg.py
+++ b/src/svg.py
@@ -11,7 +11,11 @@
 # Imports and external programs
 
 from __future__ import print_function, absolute_import
-import sys, os, subprocess, re
+import sys, os, re
+try:
+  import commands
+except ImportError:
+  import subprocess as commands
 import functools
 from vizinfo import vizinfo
 from math import sqrt,atan,cos,sin,fabs
@@ -204,7 +208,7 @@ class svg:
 
     self.single(self.file,box,atoms,bonds,tris,lines,1)
     cmd = "%s %s.svg" % (PIZZA_DISPLAY,self.file)
-    subprocess.getoutput(cmd)
+    commands.getoutput(cmd)
 
   # --------------------------------------------------------------------
 
diff --git a/src/tdump.py b/src/tdump.py
index 387e89d..711551e 100644
--- a/src/tdump.py
+++ b/src/tdump.py
@@ -11,7 +11,7 @@
 # Imports and external programs
 
 from __future__ import print_function, absolute_import
-import sys, subprocess, re, glob, types
+import sys, re, glob, types
 import functools
 from math import sqrt
 from os import popen
diff --git a/src/vcr.py b/src/vcr.py
index dae6d96..8c88c52 100644
--- a/src/vcr.py
+++ b/src/vcr.py
@@ -10,7 +10,7 @@
 
 # Imports and external programs
 
-from __future__ import absolute_import
+from __future__ import print_function, absolute_import
 try:
   from Tkinter import *
 except ImportError:
diff --git a/src/vizinfo.py b/src/vizinfo.py
index d1556d4..fab1bad 100644
--- a/src/vizinfo.py
+++ b/src/vizinfo.py
@@ -18,7 +18,7 @@
 
 # Imports and external programs
 
-from __future__ import absolute_import
+from __future__ import print_function, absolute_import
 import types
 
 # Class definition
diff --git a/src/vmd.py b/src/vmd.py
index cc5217c..3193fa2 100644
--- a/src/vmd.py
+++ b/src/vmd.py
@@ -16,7 +16,7 @@
 
 # Imports and external programs
 
-from __future__ import absolute_import
+from __future__ import print_function, absolute_import
 import types, os
 import numpy