import keyring fails with AttributeError when dbus is partially available

[jaraco]

I have a Linux environment (Ubuntu Xenial) created with python3-dbus (implicitly) installed but also python3.6 installed from the deadsnakes repo. In this environment, the dbus package is available (in /usr/local/lib/python3/dist-packages) but the underlying _dbus_bindings is not available (because the bindings were compiled for Python 3.5). In that environment, if one attempts to import dbus, one gets:

>>> import dbus
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/dbus/__init__.py", line 82, in <module>
    import dbus.types as types
  File "/usr/lib/python3/dist-packages/dbus/types.py", line 6, in <module>
    from _dbus_bindings import (
ModuleNotFoundError: No module named '_dbus_bindings'

If one attempts to import dbus again, a different error occurs:

>>> import dbus
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/dbus/__init__.py", line 81, in <module>
    import dbus.exceptions as exceptions
AttributeError: module 'dbus' has no attribute 'exceptions'

And because keyring has two modules each of which attempt to import dbus but trapping only ImportErrors, the import will fail.

>>> import keyring
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.6/dist-packages/keyring/__init__.py", line 3, in <module>
    from .core import (set_keyring, get_keyring, set_password, get_password,
  File "/usr/local/lib/python3.6/dist-packages/keyring/core.py", line 153, in <module>
    init_backend()
  File "/usr/local/lib/python3.6/dist-packages/keyring/core.py", line 66, in init_backend
    keyrings = filter(limit, backend.get_all_keyring())
  File "/usr/local/lib/python3.6/dist-packages/keyring/util/__init__.py", line 21, in wrapper
    func.always_returns = func(*args, **kwargs)
  File "/usr/local/lib/python3.6/dist-packages/keyring/backend.py", line 184, in get_all_keyring
    _load_backends()
  File "/usr/local/lib/python3.6/dist-packages/keyring/backend.py", line 142, in _load_backends
    list(map(_load_backend, backends))
  File "/usr/local/lib/python3.6/dist-packages/keyring/backend.py", line 133, in _load_backend
    mod = importlib.import_module('.' + name, package)
  File "/usr/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "/usr/local/lib/python3.6/dist-packages/keyring/backends/kwallet.py", line 12, in <module>
    import dbus
  File "/usr/lib/python3/dist-packages/dbus/__init__.py", line 81, in <module>
    import dbus.exceptions as exceptions
AttributeError: module 'dbus' has no attribute 'exceptions'

In my opinion, this is an upstream issue in either Ubuntu or dbus, but keyring should probably work around the bug.