Starting on Version 7.0 using the work done by others. Completely untested. I will be testing things, but I thought I'd get this base version up for others to give pull requests.

THIS IS ON THE MASTER BRANCH. The Master branch will be Python 3.0 from now on. While Python 2.7 support will not be deliberately broken, all efforts should now focus on Python 3.0 compatibility.

I can see a lot of work has been done. There's more to do. I've bumped the version number of everything I came across to the next major number for Python 3.0 compatibility indication.

Thanks everyone. I hope to update here at least once a week until we have a stable 7.0 release for calibre 5.0

DeDRM_plugin/ignobleepub.py

@@ -2,6 +2,7 @@
 # -*- coding: utf-8 -*-
 
 from __future__ import with_statement
+from __future__ import print_function
 
 # ignobleepub.pyw, version 4.1
 # Copyright © 2009-2010 by i♥cabbages
@@ -37,14 +38,14 @@ from __future__ import with_statement
 #   3.9 - moved unicode_argv call inside main for Windows DeDRM compatibility
 #   4.0 - Work if TkInter is missing
 #   4.1 - Import tkFileDialog, don't assume something else will import it.
+#   5.0 - Added Python 3 compatibility for calibre 5.0
 
 """
 Decrypt Barnes & Noble encrypted ePub books.
 """
-from __future__ import print_function
 
 __license__ = 'GPL v3'
-__version__ = "4.1"
+__version__ = "5.0"
 
 import sys
 import os
@@ -65,7 +66,7 @@ class SafeUnbuffered:
         if self.encoding == None:
             self.encoding = "utf-8"
     def write(self, data):
-        if isinstance(data,unicode):
+        if isinstance(data,bytes):
             data = data.encode(self.encoding,"replace")
         self.stream.write(data)
         self.stream.flush()
@@ -106,13 +107,13 @@ def unicode_argv():
             # Remove Python executable and commands if present
             start = argc.value - len(sys.argv)
             return [argv[i] for i in
-                    xrange(start, argc.value)]
+                    range(start, argc.value)]
         return [u"ineptepub.py"]
     else:
         argvencoding = sys.stdin.encoding
         if argvencoding == None:
             argvencoding = "utf-8"
-        return [arg if (type(arg) == unicode) else unicode(arg,argvencoding) for arg in sys.argv]
+        return argv
 
 
 class IGNOBLEError(Exception):
@@ -434,7 +435,7 @@ def gui_main():
             self.status['text'] = u"Decrypting..."
             try:
                 decrypt_status = decryptBook(userkey, inpath, outpath)
-            except Exception, e:
+            except Exception as e:
                 self.status['text'] = u"Error: {0}".format(e.args[0])
                 return
             if decrypt_status == 0: