[Duplicity-talk] Version 0.5.04 suggestion: improve error handling

[Michael Schneider]

When a invalid mailbox is supplied to the gmail-backend,
duplicity 0.5.04 dies with a counter-intuitive error message:

[..stuff deleted...]
  File "/usr/lib/python2.6/imaplib.py", line 1059, in _simple_command

    return self._command_complete(name, self._command(name, *args))
  File "/usr/lib/python2.6/imaplib.py", line 819, in _command
    ', '.join(Commands[name])))
error: command SEARCH illegal in state AUTH, only allowed in states SELECTED


I suggest to add the standard error-handling to select(gmail_mailbox)
to gmailimapbackend.py line 119 by changing

*** 116,122 ****

      def list(self):
          ret = []
!         self._conn.select(gmail_mailbox)

          # Going to find all the archives which have remote_dir in the From
          # address
--- 116,124 ----

      def list(self):
          ret = []
!         (result, list) = self._conn.select(gmail_mailbox)

!         if result!="OK":
!             raise Exception(list[0])

          # Going to find all the archives which have remote_dir in the From
          # address


This results in a much more usable error message (my mailbox is [Google Mail]/All Mail):

[...deleted..]
  File "/usr/lib/python2.6/site-packages/duplicity/backends/gmailimapbackend.py", line 121, in list
    raise Exception(list[0])
Exception: Unknown Mailbox: [GMail]/All Mail (Failure)

I'm not sure wether the other calls to self._conn.select(gmail_mailbox) in gmailimapbackend.py should be treated the same way. As far as I understand duplicity,  GmailImapBackend.list is called before any "dangerous" operation, so it should be sufficient to check the existence of the mailbox there. 

Cheers,
Michael