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/askfolder_ed.py

@@ -29,6 +29,8 @@
 # FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 # DEALINGS IN THE SOFTWARE.
 
+# Adjusted for Python 3, September 2020
+
 """
 AskFolder(...) -- Ask the user to select a folder Windows specific
 """
@@ -164,15 +166,15 @@ def AskFolder(
     def BrowseCallback(hwnd, uMsg, lParam, lpData):
         if uMsg == BFFM_INITIALIZED:
             if actionButtonLabel:
-                label = unicode(actionButtonLabel, errors='replace')
+                label = actionButtonLabel.decode('utf-8', 'replace')
                 user32.SendMessageW(hwnd, BFFM_SETOKTEXT, 0, label)
             if cancelButtonLabel:
-                label = unicode(cancelButtonLabel, errors='replace')
+                label = cancelButtonLabel.decode('utf-8', 'replace')
                 cancelButton = user32.GetDlgItem(hwnd, IDCANCEL)
                 if cancelButton:
                     user32.SetWindowTextW(cancelButton, label)
             if windowTitle:
-                title = unicode(windowTitle, erros='replace')
+                title = windowTitle.decode('utf-8', 'replace')
                 user32.SetWindowTextW(hwnd, title)
             if defaultLocation:
                 user32.SendMessageW(hwnd, BFFM_SETSELECTIONW, 1, defaultLocation.replace('/', '\\'))