Add ruff linting

Configure ruff in pyproject.toml and apply its fixes: modern annotations
(X | None, builtin generics, collections.abc), sorted imports, explicit
stacklevel in test warnings.

simple_backup/simple_backup.py

@@ -14,27 +14,27 @@ Classes:
 # Avoid evaluating annotations at definition time, as they reference optional modules (paramiko)
 from __future__ import annotations
 
-# Import libraries
-import sys
-import os
-import pwd
-import io
-import re
-from typing import Callable, Iterator, List, Optional, ParamSpec, TypedDict, TypeVar
-import warnings
-from functools import wraps
-from shutil import get_terminal_size, rmtree, which
-import shlex
 import argparse
 import configparser
+import io
 import logging
-from logging import StreamHandler
-from timeit import default_timer
-from subprocess import Popen, PIPE, STDOUT
+import os
+import pwd
+import re
+import shlex
+import sys
+import warnings
+from collections.abc import Callable, Iterator
 from datetime import datetime
-from tempfile import mkstemp
+from functools import wraps
 from getpass import GetPassWarning, getpass
 from glob import glob
+from logging import StreamHandler
+from shutil import get_terminal_size, rmtree, which
+from subprocess import PIPE, STDOUT, Popen
+from tempfile import mkstemp
+from timeit import default_timer
+from typing import ParamSpec, TypedDict, TypeVar
 
 try:
     import paramiko
@@ -204,9 +204,9 @@ class Backup:
             Perform the backup
     """
 
-    def __init__(self, inputs: Optional[List[str]], output: Optional[str], exclude: Optional[List[str]],
-                 keep: Optional[int], options: str,
-                 ssh_host: Optional[str] = None, ssh_user: Optional[str] = None, ssh_keyfile: Optional[str] = None,
+    def __init__(self, inputs: list[str] | None, output: str | None, exclude: list[str] | None,
+                 keep: int | None, options: str,
+                 ssh_host: str | None = None, ssh_user: str | None = None, ssh_keyfile: str | None = None,
                  remote_sudo: bool = False, remove_before: bool = False, verbose: bool = False,
                  progress: bool = False) -> None:
         # Missing values are reported by check_params()
@@ -228,7 +228,7 @@ class Backup:
         self._inputs_path = ''
         self._exclude_path = ''
         self._remote = False
-        self._ssh: Optional[paramiko.client.SSHClient] = None
+        self._ssh: paramiko.client.SSHClient | None = None
         self._password_auth = False
         self._removed_count = 0
 
@@ -281,7 +281,7 @@ class Backup:
 
         return 0
 
-    def _resolve_remote_path(self, path: str) -> Optional[str]:
+    def _resolve_remote_path(self, path: str) -> str | None:
         """Return the absolute path of a directory on the server, or None if it doesn't exist"""
 
         assert self._ssh is not None
@@ -450,7 +450,7 @@ class Backup:
             except IndexError:
                 logger.info('No previous backups available')
 
-    def _ssh_connect(self, homedir: str = '') -> Optional[paramiko.client.SSHClient]:
+    def _ssh_connect(self, homedir: str = '') -> paramiko.client.SSHClient | None:
         try:
             ssh = paramiko.SSHClient()
         except NameError:
@@ -469,7 +469,7 @@ class Backup:
             if connected is None:
                 ssh.close()
 
-    def _ssh_login(self, ssh: paramiko.client.SSHClient, homedir: str) -> Optional[paramiko.client.SSHClient]:
+    def _ssh_login(self, ssh: paramiko.client.SSHClient, homedir: str) -> paramiko.client.SSHClient | None:
         try:
             ssh.load_host_keys(filename=f'{homedir}/.ssh/known_hosts')
         except FileNotFoundError:
@@ -553,7 +553,7 @@ class Backup:
 
         return ssh
 
-    def _load_ssh_key(self) -> Optional[paramiko.PKey]:
+    def _load_ssh_key(self) -> paramiko.PKey | None:
         try:
             return paramiko.PKey.from_path(self.ssh_keyfile)
         except TypeError:
@@ -808,7 +808,7 @@ def _read_records(stream: io.BufferedIOBase) -> Iterator[str]:
         yield buffer.decode('utf-8', errors='replace')
 
 
-def _detect_user() -> Optional[str]:
+def _detect_user() -> str | None:
     if os.geteuid() == 0:
         return os.getenv('SUDO_USER') or os.getenv('DOAS_USER')
 
@@ -873,8 +873,8 @@ def _expand_home(path: str, user: str) -> str:
     return os.path.expanduser(path)
 
 
-def _expand_inputs(inputs: List[str], user: Optional[str] = None) -> List[str]:
-    expanded_inputs: List[str] = []
+def _expand_inputs(inputs: list[str], user: str | None = None) -> list[str]:
+    expanded_inputs: list[str] = []
 
     for i in inputs:
         if i == '':
@@ -900,13 +900,13 @@ def _expand_inputs(inputs: List[str], user: Optional[str] = None) -> List[str]:
 class ConfigArgs(TypedDict):
     """Values read from the configuration file"""
 
-    inputs: Optional[List[str]]
-    output: Optional[str]
-    exclude: Optional[List[str]]
+    inputs: list[str] | None
+    output: str | None
+    exclude: list[str] | None
     keep: int
-    ssh_host: Optional[str]
-    ssh_user: Optional[str]
-    ssh_keyfile: Optional[str]
+    ssh_host: str | None
+    ssh_user: str | None
+    ssh_keyfile: str | None
     remote_sudo: bool
     numeric_ids: bool
 
@@ -919,7 +919,7 @@ def _get_bool(config: configparser.ConfigParser, key: str) -> bool:
     return config.getboolean('server', key)
 
 
-def _read_config(config_file: str, user: Optional[str] = None) -> ConfigArgs:
+def _read_config(config_file: str, user: str | None = None) -> ConfigArgs:
     config_args: ConfigArgs = {'inputs': None,
                                'output': None,
                                'exclude': None,