Add compatibility with Python 3 (keeping compatibility with Python 2.7)

--- gtk+-2.24.32/gtk/gtk-builder-convert       (original)
+++ gtk+-2.24.32/gtk/gtk-builder-convert       (refactored)
@@ -36,10 +36,11 @@
 
 Report bugs to http://bugzilla.gnome.org/."""
 
+from __future__ import print_function
 import getopt
 import os
 import sys
-
+import subprocess
 from xml.dom import minidom, Node
 
 DIALOGS = ['GtkDialog',
@@ -47,13 +48,6 @@
            'GtkMessageDialog']
 WINDOWS = ['GtkWindow'] + DIALOGS
 
-# The subprocess is only available in Python 2.4+
-try:
-    import subprocess
-    subprocess # pyflakes
-except ImportError:
-    subprocess = None
-
 def get_child_nodes(node):
     assert node.tagName == 'object'
     nodes = []
@@ -167,7 +161,11 @@
 
     def to_xml(self):
         xml = self._dom.toprettyxml("", "")
-        return xml.encode('utf-8')
+        if sys.version_info < (3, 0):
+            # Python 2: convert with explicit encoding
+            # (For Python 3, the result is left as text)
+            xml = xml.encode('utf-8')
+        return xml
 
     #
     # Private
@@ -259,7 +257,7 @@
         for node in objects:
             self._convert(node.getAttribute("class"), node)
             if self._get_object(node.getAttribute('id')) is not None:
-		print "WARNING: duplicate id \"" + node.getAttribute('id') + "\""
+                print("WARNING: duplicate id \"" + node.getAttribute('id') + "\"")
             self.objects[node.getAttribute('id')] = node
 
         # Convert Gazpachos UI tag
@@ -272,13 +270,9 @@
 
         # Output the newly created root objects and sort them
         # by attribute id
-        # FIXME: Use sorted(self.root_objects,
-        #                   key=lambda n: n.getAttribute('id'),
-        #                   reverse=True):
-        # when we can depend on python 2.4 or higher
-        root_objects = self.root_objects[:]
-        root_objects.sort(lambda a, b: cmp(b.getAttribute('id'),
-                                           a.getAttribute('id')))
+        root_objects = sorted(self.root_objects,
+                              key=lambda n: n.getAttribute('id'),
+                              reverse=True)
         for obj in root_objects:
             self._interface.childNodes.insert(0, obj)
 
@@ -461,8 +455,8 @@
             if signal_name in ['activate', 'toggled']:
                 action.appendChild(signal)
             else:
-                print 'Unhandled signal %s::%s' % (node.getAttribute('class'),
-                                                   signal_name)
+                print('Unhandled signal %s::%s' % (node.getAttribute('class'),
+                                                   signal_name))
 
         if not uimgr.childNodes:
             child = self._dom.createElement('child')
@@ -481,8 +475,8 @@
         for accelerator in get_accelerator_nodes(node):
             signal_name = accelerator.getAttribute('signal')
             if signal_name != 'activate':
-                print 'Unhandled accelerator signal for %s::%s' % (
-                    node.getAttribute('class'), signal_name)
+                print('Unhandled accelerator signal for %s::%s' % (
+                    node.getAttribute('class'), signal_name))
                 continue
             accelerator.removeAttribute('signal')
             child.appendChild(accelerator)
@@ -741,13 +735,14 @@
 
     s = subprocess.Popen([filename, '--format', '-'],
                          stdin=subprocess.PIPE,
-                         stdout=subprocess.PIPE)
+                         stdout=subprocess.PIPE,
+                         universal_newlines=True)
     s.stdin.write(output)
     s.stdin.close()
     return s.stdout.read()
 
 def usage():
-    print __doc__
+    print(__doc__)
 
 def main(args):
     try:
@@ -788,10 +783,10 @@
 
     xml = _indent(conv.to_xml())
     if output_filename == "-":
-        print xml
+        print(xml)
     else:
         open(output_filename, 'w').write(xml)
-        print "Wrote", output_filename
+        print("Wrote", output_filename)
 
     return 0