style: modernize type hints, a few more f-strings

I used:
```
ruff --select=UP,F  --unsafe-fixes --fix *.py {coverage,tests,ci}/*.py
```
and then fixed a few "unused imports" that are actually needed by hand.

Author: nedbat

coverage/__init__.py

@@ -39,4 +39,3 @@
 # On Windows, we encode and decode deep enough that something goes wrong and
 # the encodings.utf_8 module is loaded and then unloaded, I don't know why.
 # Adding a reference here prevents it from being unloaded.  Yuk.
-import encodings.utf_8      # pylint: disable=wrong-import-position, wrong-import-order

coverage/annotate.py

@@ -8,7 +8,7 @@
 import os
 import re
 
-from typing import Iterable, Optional, TYPE_CHECKING
+from typing import Iterable, TYPE_CHECKING
 
 from coverage.files import flat_rootname
 from coverage.misc import ensure_dir, isolate_module
@@ -48,12 +48,12 @@ class AnnotateReporter:
     def __init__(self, coverage: Coverage) -> None:
         self.coverage = coverage
         self.config = self.coverage.config
-        self.directory: Optional[str] = None
+        self.directory: str | None = None
 
     blank_re = re.compile(r"\s*(#|$)")
     else_re = re.compile(r"\s*else\s*:\s*(#|$)")
 
-    def report(self, morfs: Optional[Iterable[TMorf]], directory: Optional[str] = None) -> None:
+    def report(self, morfs: Iterable[TMorf] | None, directory: str | None = None) -> None:
         """Run the report.
 
         See `coverage.report()` for arguments.

coverage/cmdline.py

@@ -14,7 +14,7 @@
 import textwrap
 import traceback
 
-from typing import cast, Any, List, NoReturn, Optional, Tuple
+from typing import cast, Any, NoReturn
 
 import coverage
 from coverage import Coverage
@@ -281,7 +281,7 @@ class OptionParserError(Exception):
         """Used to stop the optparse error handler ending the process."""
         pass
 
-    def parse_args_ok(self, args: List[str]) -> Tuple[bool, Optional[optparse.Values], List[str]]:
+    def parse_args_ok(self, args: list[str]) -> tuple[bool, optparse.Values | None, list[str]]:
         """Call optparse.parse_args, but return a triple:
 
         (ok, options, args)
@@ -317,9 +317,9 @@ class CmdOptionParser(CoverageOptionParser):
     def __init__(
         self,
         action: str,
-        options: List[optparse.Option],
+        options: list[optparse.Option],
         description: str,
-        usage: Optional[str] = None,
+        usage: str | None = None,
     ):
         """Create an OptionParser for a coverage.py command.
 
@@ -549,9 +549,9 @@ def get_prog_name(self) -> str:
 
 
 def show_help(
-    error: Optional[str] = None,
-    topic: Optional[str] = None,
-    parser: Optional[optparse.OptionParser] = None,
+    error: str | None = None,
+    topic: str | None = None,
+    parser: optparse.OptionParser | None = None,
 ) -> None:
     """Display an error message, or the named topic."""
     assert error or topic or parser
@@ -605,7 +605,7 @@ def __init__(self) -> None:
         self.global_option = False
         self.coverage: Coverage
 
-    def command_line(self, argv: List[str]) -> int:
+    def command_line(self, argv: list[str]) -> int:
         """The bulk of the command line interface to coverage.py.
 
         `argv` is the argument list to process.
@@ -620,7 +620,7 @@ def command_line(self, argv: List[str]) -> int:
 
         # The command syntax we parse depends on the first argument.  Global
         # switch syntax always starts with an option.
-        parser: Optional[optparse.OptionParser]
+        parser: optparse.OptionParser | None
         self.global_option = argv[0].startswith("-")
         if self.global_option:
             parser = GlobalOptionParser()
@@ -772,7 +772,7 @@ def command_line(self, argv: List[str]) -> int:
     def do_help(
         self,
         options: optparse.Values,
-        args: List[str],
+        args: list[str],
         parser: optparse.OptionParser,
     ) -> bool:
         """Deal with help requests.
@@ -807,7 +807,7 @@ def do_help(
 
         return False
 
-    def do_run(self, options: optparse.Values, args: List[str]) -> int:
+    def do_run(self, options: optparse.Values, args: list[str]) -> int:
         """Implementation of 'coverage run'."""
 
         if not args:
@@ -866,7 +866,7 @@ def do_run(self, options: optparse.Values, args: List[str]) -> int:
 
         return OK
 
-    def do_debug(self, args: List[str]) -> int:
+    def do_debug(self, args: list[str]) -> int:
         """Implementation of 'coverage debug'."""
 
         if not args:
@@ -899,7 +899,7 @@ def do_debug(self, args: List[str]) -> int:
         return OK
 
 
-def unshell_list(s: str) -> Optional[List[str]]:
+def unshell_list(s: str) -> list[str] | None:
     """Turn a command-line argument into a list."""
     if not s:
         return None
@@ -913,7 +913,7 @@ def unshell_list(s: str) -> Optional[List[str]]:
     return s.split(",")
 
 
-def unglob_args(args: List[str]) -> List[str]:
+def unglob_args(args: list[str]) -> list[str]:
     """Interpret shell wildcards for platforms that need it."""
     if env.WINDOWS:
         globbed = []
@@ -958,7 +958,7 @@ def unglob_args(args: List[str]) -> List[str]:
 }
 
 
-def main(argv: Optional[List[str]] = None) -> Optional[int]:
+def main(argv: list[str] | None = None) -> int | None:
     """The main entry point to coverage.py.
 
     This is installed as the script entry point.
@@ -997,8 +997,8 @@ def main(argv: Optional[List[str]] = None) -> Optional[int]:
     original_main = main
 
     def main(                                               # pylint: disable=function-redefined
-        argv: Optional[List[str]] = None,
-    ) -> Optional[int]:
+        argv: list[str] | None = None,
+    ) -> int | None:
         """A wrapper around main that profiles."""
         profiler = SimpleLauncher.launch()
         try:

coverage/collector.py

@@ -11,7 +11,7 @@
 
 from types import FrameType
 from typing import (
-    cast, Any, Callable, Dict, List, Mapping, Optional, Set, Type, TypeVar,
+    cast, Any, Callable, Dict, List, Mapping, Set, TypeVar,
 )
 
 from coverage import env
@@ -70,7 +70,7 @@ class Collector:
     # The stack of active Collectors.  Collectors are added here when started,
     # and popped when stopped.  Collectors on the stack are paused when not
     # the top, and resumed when they become the top again.
-    _collectors: List[Collector] = []
+    _collectors: list[Collector] = []
 
     # The concurrency settings we support here.
     LIGHT_THREADS = {"greenlet", "eventlet", "gevent"}
@@ -79,12 +79,12 @@ def __init__(
         self,
         should_trace: Callable[[str, FrameType], TFileDisposition],
         check_include: Callable[[str, FrameType], bool],
-        should_start_context: Optional[Callable[[FrameType], Optional[str]]],
+        should_start_context: Callable[[FrameType], str | None] | None,
         file_mapper: Callable[[str], str],
         timid: bool,
         branch: bool,
         warn: TWarnFn,
-        concurrency: List[str],
+        concurrency: list[str],
         metacov: bool,
     ) -> None:
         """Create a collector.
@@ -136,16 +136,16 @@ def __init__(
 
         self.covdata: CoverageData
         self.threading = None
-        self.static_context: Optional[str] = None
+        self.static_context: str | None = None
 
         self.origin = short_stack()
 
         self.concur_id_func = None
 
-        self._trace_class: Type[TracerCore]
-        self.file_disposition_class: Type[TFileDisposition]
+        self._trace_class: type[TracerCore]
+        self.file_disposition_class: type[TFileDisposition]
 
-        core: Optional[str]
+        core: str | None
         if timid:
             core = "pytrace"
         else:
@@ -240,7 +240,7 @@ def __init__(
     def __repr__(self) -> str:
         return f"<Collector at {id(self):#x}: {self.tracer_name()}>"
 
-    def use_data(self, covdata: CoverageData, context: Optional[str]) -> None:
+    def use_data(self, covdata: CoverageData, context: str | None) -> None:
         """Use `covdata` for recording data."""
         self.covdata = covdata
         self.static_context = context
@@ -268,9 +268,9 @@ def reset(self) -> None:
 
         # A dictionary mapping file names to file tracer plugin names that will
         # handle them.
-        self.file_tracers: Dict[str, str] = {}
+        self.file_tracers: dict[str, str] = {}
 
-        self.disabled_plugins: Set[str] = set()
+        self.disabled_plugins: set[str] = set()
 
         # The .should_trace_cache attribute is a cache from file names to
         # coverage.FileDisposition objects, or None.  When a file is first
@@ -301,7 +301,7 @@ def reset(self) -> None:
             self.should_trace_cache = {}
 
         # Our active Tracers.
-        self.tracers: List[TracerCore] = []
+        self.tracers: list[TracerCore] = []
 
         self._clear_data()
 
@@ -342,12 +342,12 @@ def _start_tracer(self) -> TTraceFn | None:
     #
     # New in 3.12: threading.settrace_all_threads: https://github.com/python/cpython/pull/96681
 
-    def _installation_trace(self, frame: FrameType, event: str, arg: Any) -> Optional[TTraceFn]:
+    def _installation_trace(self, frame: FrameType, event: str, arg: Any) -> TTraceFn | None:
         """Called on new threads, installs the real tracer."""
         # Remove ourselves as the trace function.
         sys.settrace(None)
         # Install the real tracer.
-        fn: Optional[TTraceFn] = self._start_tracer()
+        fn: TTraceFn | None = self._start_tracer()
         # Invoke the real trace function with the current event, to be sure
         # not to lose an event.
         if fn:
@@ -444,9 +444,9 @@ def _activity(self) -> bool:
         """
         return any(tracer.activity() for tracer in self.tracers)
 
-    def switch_context(self, new_context: Optional[str]) -> None:
+    def switch_context(self, new_context: str | None) -> None:
         """Switch to a new dynamic context."""
-        context: Optional[str]
+        context: str | None
         self.flush_data()
         if self.static_context:
             context = self.static_context
@@ -471,7 +471,7 @@ def cached_mapped_file(self, filename: str) -> str:
         """A locally cached version of file names mapped through file_mapper."""
         return self.file_mapper(filename)
 
-    def mapped_file_dict(self, d: Mapping[str, T]) -> Dict[str, T]:
+    def mapped_file_dict(self, d: Mapping[str, T]) -> dict[str, T]:
         """Return a dict like d, but with keys modified by file_mapper."""
         # The call to list(items()) ensures that the GIL protects the dictionary
         # iterator against concurrent modifications by tracers running
@@ -511,7 +511,7 @@ def flush_data(self) -> bool:
                 # Unpack the line number pairs packed into integers.  See
                 # tracer.c:CTracer_record_pair for the C code that creates
                 # these packed ints.
-                arc_data: Dict[str, List[TArc]] = {}
+                arc_data: dict[str, list[TArc]] = {}
                 packed_data = cast(Dict[str, Set[int]], self.data)
 
                 # The list() here and in the inner loop are to get a clean copy