ChainerBackend not deleting password from lower priority backend

[jim-easterbrook]

Describe the bug
Using kdewallet I can see old keyring passwords listed in "Secret Service". New keyring passwords are listed under the "system" passed to set_password. I assume this is because I previously did not have keyring.backends.kwallet.DBusKeyring installed.

$ python3.11 -m keyring --list-backends
keyring.backends.chainer.ChainerBackend (priority: 10)
keyring.backends.kwallet.DBusKeyring (priority: 5.1)
keyring.backends.SecretService.Keyring (priority: 5)
keyring.backends.fail.Keyring (priority: 0)

$ python3.11 -m keyring get system username correctly finds the old passwords. $ python3.11 -m keyring del system username fails as follows:

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/__main__.py", line 4, in <module>
    cli.main()
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/cli.py", line 216, in main
    return cli.run(argv)
           ^^^^^^^^^^^^^
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/cli.py", line 120, in run
    return method()
           ^^^^^^^^
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/cli.py", line 157, in do_del
    delete_password(self.service, self.username)
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/core.py", line 73, in delete_password
    get_keyring().delete_password(service_name, username)
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/backends/chainer.py", line 63, in delete_password
    return keyring.delete_password(service, username)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/backends/kwallet.py", line 150, in delete_password
    raise PasswordDeleteError("Password not found")
keyring.errors.PasswordDeleteError: Password not found

Expected behavior
I would expect to be able to delete any password that I can read.

Environment

• OS: openSUSE 15.6

$ python3.11 -m pip list | grep keyring
keyring                       25.4.1

$ python3.11 -m keyring --list-backends
keyring.backends.chainer.ChainerBackend (priority: 10)
keyring.backends.kwallet.DBusKeyring (priority: 5.1)
keyring.backends.SecretService.Keyring (priority: 5)
keyring.backends.fail.Keyring (priority: 0)

[jim-easterbrook]

How to reproduce:

$ python3.11 -m keyring -b keyring.backends.SecretService.Keyring set testing test
Password for 'test' in 'testing': 
$ python3.11 -m keyring get testing test
password
$ python3.11 -m keyring del testing test
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/__main__.py", line 4, in <module>
    cli.main()
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/cli.py", line 216, in main
    return cli.run(argv)
           ^^^^^^^^^^^^^
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/cli.py", line 120, in run
    return method()
           ^^^^^^^^
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/cli.py", line 157, in do_del
    delete_password(self.service, self.username)
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/core.py", line 73, in delete_password
    get_keyring().delete_password(service_name, username)
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/backends/chainer.py", line 63, in delete_password
    return keyring.delete_password(service, username)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jim/.local/lib/python3.11/site-packages/keyring/backends/kwallet.py", line 150, in delete_password
    raise PasswordDeleteError("Password not found")
keyring.errors.PasswordDeleteError: Password not found

Of course I can delete the password by specifying the backend with -b, but I'd prefer not to worry about backends in my programmatic use of python-keyring.

[jaraco]

That seems like a bug to me. I see that the chainer's behavior is to suppress NotImplementedError but not other errors from the chained backends. Probably it should also suppress PasswordDeleteError or maybe there should be a separate class of exception for PasswordNotFound so that the chainer can discern between a failure and a non-existent password. Would you be willing to work on a patch?