NameError: global name 'Dropbox' is not defined

[Pedro Gimeno]

Using the current head (1334 at the time of writing), I'm getting an exception when trying to backup using the dpbx scheme:

Traceback (innermost last):
  File "./duplicity.py", line 1668, in <module>
    with_tempdir(main)
  File "./duplicity.py", line 1654, in with_tempdir
    fn()
  File "./duplicity.py", line 1488, in main
    action = commandline.ProcessCommandLine(sys.argv[1:])
  File "<redacted>/duplicity/commandline.py", line 1180, in ProcessCommandLine
    backup, local_pathname = set_backend(args[0], args[1])
  File "<redacted>/duplicity/commandline.py", line 1051, in set_backend
    globals.backend = backend.get_backend(bend)
  File "<redacted>/duplicity/backend.py", line 223, in get_backend
    obj = get_backend_object(url_string)
  File "<redacted>/duplicity/backend.py", line 209, in get_backend_object
    return factory(pu)
  File "<redacted>/duplicity/backends/dpbxbackend.py", line 110, in __init__
    self.login()
  File "<redacted>/duplicity/backends/dpbxbackend.py", line 163, in login
    self.api_client = Dropbox(self.load_access_token())
 NameError: global name 'Dropbox' is not defined

The problem was introduced with the removal of the globals in revision 1297:

https://bazaar.launchpad.net/~duplicity-team/duplicity/0.8-series/revision/1297#duplicity/backends/dpbxbackend.py

Re-adding the globals makes the problem disappear. I have NOT checked other backends modified in the same revision for similar problems, so it's possible that others are affected.

[Pedro Gimeno (pgimeno)]

For clarity, I've attached a patch that reverts the removal of the globals.

Without this patch, the imported identifiers are local to the __init__() constructor where the import statements are, and the rest of the code can't use them.