diff --git a/lib/cli_command_parser/context.py b/lib/cli_command_parser/context.py
index 0c0facfa..f728eedc 100644
--- a/lib/cli_command_parser/context.py
+++ b/lib/cli_command_parser/context.py
@@ -46,7 +46,7 @@ class Context(AbstractContextManager):  # Extending AbstractContextManager to ma
     config: CommandConfig
     prog: OptStr = None
     allow_argv_prog: Bool = True
-    _command_obj: CommandObj = None
+    _command_obj: CommandObj | None = None
     _terminal_width: int | None
     _provided: dict[ParamOrGroup, int]
 
@@ -56,8 +56,8 @@ def __init__(
         command_cls: CommandType | None = None,
         *,
         parent: Context | None = None,
-        config: AnyConfig = None,
-        terminal_width: int = None,
+        config: AnyConfig | None = None,
+        terminal_width: int | None = None,
         allow_argv_prog: Bool = None,
         command: CommandObj | None = None,
         **kwargs,
@@ -100,7 +100,7 @@ def _set_argv(self, prog: OptStr, argv: Argv):
         self.remaining = list(self.argv)
 
     def _sub_context(
-        self, command_cls: CommandType, argv: Argv = None, command: CommandObj = None, **kwargs
+        self, command_cls: CommandType, argv: Argv = None, command: CommandObj | None = None, **kwargs
     ) -> Context:
         return self.__class__(
             self.remaining if argv is None else argv,
@@ -151,7 +151,7 @@ def terminal_width(self) -> int:
 
     def get_parsed(
         self,
-        command: Command = None,
+        command: Command | None = None,
         *,
         exclude: Collection[Parameter] = (),
         recursive: Bool = True,
@@ -443,7 +443,7 @@ def get_current_context(silent: bool = False) -> Context | None:
 
 
 def get_or_create_context(
-    command_cls: CommandType, argv: Argv = None, *, command: CommandObj = None, **kwargs
+    command_cls: CommandType, argv: Argv = None, *, command: CommandObj | None = None, **kwargs
 ) -> Context:
     """
     Used internally by Commands to re-use an existing user-activated Context, or to create a new Context if there was
@@ -469,7 +469,7 @@ def get_context(command: Command) -> Context:
 
 
 def get_parsed(
-    command: Command, to_call: Callable = None, default: Any = None, include_defaults: Bool = True
+    command: Command, to_call: Callable | None = None, default: Any = None, include_defaults: Bool = True
 ) -> dict[str, Any]:
     """
     Provides a way to obtain all of the arguments that were parsed for the given Command as a dictionary.
diff --git a/lib/cli_command_parser/conversion/argparse_ast.py b/lib/cli_command_parser/conversion/argparse_ast.py
index 6c7b26b2..8128dcbe 100644
--- a/lib/cli_command_parser/conversion/argparse_ast.py
+++ b/lib/cli_command_parser/conversion/argparse_ast.py
@@ -35,7 +35,7 @@ class Script:
     _parser_classes = {}
     path: Path | None
 
-    def __init__(self, src_text: str, smart_loop_handling: bool = True, path: PathLike = None):
+    def __init__(self, src_text: str, smart_loop_handling: bool = True, path: PathLike | None = None):
         self.smart_loop_handling = smart_loop_handling
         self._parsers = []
         self.path = Path(path) if path else None
@@ -143,13 +143,15 @@ def _add_visit_func(cls, name: str) -> bool:
         cls.visit_funcs.add(name)
         return True
 
-    def __init_subclass__(cls, represents: RepresentedCallable = None, **kwargs):
+    def __init_subclass__(cls, represents: RepresentedCallable | None = None, **kwargs):
         super().__init_subclass__(**kwargs)
         if represents:
             cls.represents = represents
             cls._sig = None
 
-    def __init__(self, node: InitNode, parent: AstCallable | Script, tracked_refs: TrackedRefMap, call: Call = None):
+    def __init__(
+        self, node: InitNode, parent: AstCallable | Script, tracked_refs: TrackedRefMap, call: Call | None = None
+    ):
         self.init_node = node
         if not call:
             call = node.value if isinstance(node, Assign) else node  # type: Call
@@ -253,7 +255,9 @@ def __init_subclass__(cls, children: Collection[str] = (), **kwargs):
         if children:
             cls._children = (*cls._children, *children)
 
-    def __init__(self, node: InitNode, parent: AstCallable | Script, tracked_refs: TrackedRefMap, call: Call = None):
+    def __init__(
+        self, node: InitNode, parent: AstCallable | Script, tracked_refs: TrackedRefMap, call: Call | None = None
+    ):
         super().__init__(node, parent, tracked_refs, call)
         self.args = []
         self.groups = []
@@ -314,7 +318,9 @@ class AstArgumentParser(ArgCollection, represents=ArgumentParser, children=('sub
     sub_parsers: list[SubParser]
     add_subparsers = AddVisitedChild(SubparsersAction, '_subparsers_actions')
 
-    def __init__(self, node: InitNode, parent: AstCallable | Script, tracked_refs: TrackedRefMap, call: Call = None):
+    def __init__(
+        self, node: InitNode, parent: AstCallable | Script, tracked_refs: TrackedRefMap, call: Call | None = None
+    ):
         super().__init__(node, parent, tracked_refs, call)
         self._subparsers_actions = []
         # Note: sub_parsers aren't included in grouped_children since they need different handling during conversion
@@ -324,7 +330,9 @@ def __repr__(self) -> str:
         sub_parsers = len(self.sub_parsers)
         return f'<{self.__class__.__name__}[{sub_parsers=}]: ``{self.init_call_repr()}``>'
 
-    def _add_subparser(self, node: InitNode, call: Call, tracked_refs: TrackedRefMap, sub_parser_cls: ParserCls = None):
+    def _add_subparser(
+        self, node: InitNode, call: Call, tracked_refs: TrackedRefMap, sub_parser_cls: ParserCls | None = None
+    ):
         # Using default of None since the class hasn't been defined at the time it would need to be set as default
         return self._add_child(sub_parser_cls or SubParser, self.sub_parsers, node, call, tracked_refs)
 
diff --git a/lib/cli_command_parser/conversion/command_builder.py b/lib/cli_command_parser/conversion/command_builder.py
index 8880532d..491de05b 100644
--- a/lib/cli_command_parser/conversion/command_builder.py
+++ b/lib/cli_command_parser/conversion/command_builder.py
@@ -33,11 +33,11 @@ def convert_script(script: Script, add_methods: bool = False) -> str:
 
 
 class Converter(Generic[AC], ABC):
-    converts: Type[AC] = None
+    converts: Type[AC] | None = None
     newline_between_members: bool = False
     _ac_converter_map = {}
 
-    def __init_subclass__(cls, converts: Type[AC] = None, newline_between_members: bool = None, **kwargs):
+    def __init_subclass__(cls, converts: Type[AC] | None = None, newline_between_members: bool | None = None, **kwargs):
         super().__init_subclass__(**kwargs)
         if converts:
             cls.converts = converts
@@ -165,8 +165,8 @@ class ParserConverter(CollectionConverter[AstArgumentParser], converts=AstArgume
     def __init__(
         self,
         parser: AstArgumentParser,
-        parent: ParserConverter = None,
-        counter: count = None,
+        parent: ParserConverter | None = None,
+        counter: count | None = None,
         *,
         add_methods: bool = False,
     ):
diff --git a/lib/cli_command_parser/documentation.py b/lib/cli_command_parser/documentation.py
index c985c539..2693d531 100644
--- a/lib/cli_command_parser/documentation.py
+++ b/lib/cli_command_parser/documentation.py
@@ -22,7 +22,7 @@
 from .formatting.restructured_text import MODULE_TEMPLATE, rst_header, rst_toc_tree
 
 if TYPE_CHECKING:
-    from .typing import Bool, CommandCls, PathLike, Strings
+    from .typing import Bool, CommandCls, OptStr, PathLike, Strings
 
     Commands = dict[str, CommandCls]
 
@@ -34,14 +34,14 @@
 
 
 def render_script_rst(
-    path: PathLike, top_only: Bool = True, fix_name: Bool = True, fix_name_func: NameFunc = None
+    path: PathLike, top_only: Bool = True, fix_name: Bool = True, fix_name_func: NameFunc | None = None
 ) -> str:
     """Load all Commands from the file with the given path, and generate a single RST string based on those Commands"""
     commands = load_commands(path, top_only)
     return _render_commands_rst(commands, fix_name, fix_name_func)
 
 
-def render_command_rst(command: CommandCls, fix_name: Bool = True, fix_name_func: NameFunc = None) -> str:
+def render_command_rst(command: CommandCls, fix_name: Bool = True, fix_name_func: NameFunc | None = None) -> str:
     """
     :param command: The :class:`.Command` to document
     :param fix_name: Whether the file name should be re-formatted from CamelCase / snake_case to separate Title Case
@@ -53,7 +53,7 @@ def render_command_rst(command: CommandCls, fix_name: Bool = True, fix_name_func
         return get_formatter(command).format_rst(fix_name, fix_name_func)
 
 
-def _render_commands_rst(commands: Commands, fix_name: Bool = True, fix_name_func: NameFunc = None) -> str:
+def _render_commands_rst(commands: Commands, fix_name: Bool = True, fix_name_func: NameFunc | None = None) -> str:
     # This could be better, but it's relatively unlikely to have multiple top level commands in a script...
     # For the same reason that main() does not try to pick one, this will just combine all of them.
     parts = []
@@ -199,7 +199,7 @@ def __init__(
         newline: str = '\n',
         ext: str = '.rst',
         module_template: str = MODULE_TEMPLATE,
-        skip_modules: Strings = None,
+        skip_modules: Strings | None = None,
     ):
         self.output_dir = Path(output_dir)
         self.dry_run = dry_run
@@ -212,9 +212,9 @@ def __init__(
     def document_script(
         self,
         path: Path,
-        subdir: str = None,
-        name: str = None,
-        replacements: Mapping[str, str] = None,
+        subdir: OptStr = None,
+        name: OptStr = None,
+        replacements: Mapping[str, str] | None = None,
         top_only: Bool = True,
         **kwargs,
     ) -> str:
@@ -253,13 +253,13 @@ def document_script(
     def document_scripts(
         self,
         paths: Iterable[Path],
-        subdir: str = None,
+        subdir: OptStr = None,
         top_only: Bool = True,
         *,
-        index_name: str = None,
-        index_header: str = None,
-        index_subdir: str = None,
-        caption: str = None,
+        index_name: OptStr = None,
+        index_header: OptStr = None,
+        index_subdir: OptStr = None,
+        caption: OptStr = None,
         **kwargs,
     ):
         names = [self.document_script(path, subdir, top_only=top_only, **kwargs) for path in paths]
@@ -269,7 +269,7 @@ def document_scripts(
                 name, index_header or name.title(), names, content_subdir=subdir, caption=caption, subdir=index_subdir
             )
 
-    def document_module(self, module: str, subdir: str = None):
+    def document_module(self, module: str, subdir: OptStr = None):
         """
         Generate an RST file to document a Python module.
 
@@ -285,13 +285,13 @@ def document_package(
         self,
         pkg_name: str,
         pkg_path: Path,
-        subdir: str = None,
+        subdir: OptStr = None,
         *,
-        name: str = None,
-        header: str = None,
+        name: OptStr = None,
+        header: OptStr = None,
         index: Bool = True,
         empty: Bool = False,
-        caption: str = None,
+        caption: OptStr = None,
         max_depth: int = 4,
     ) -> list[str]:
         """
@@ -331,7 +331,9 @@ def document_package(
         )
         return contents
 
-    def _generate_code_rsts(self, pkg_name: str, pkg_path: Path, subdir: str = None, max_depth: int = 4) -> list[str]:
+    def _generate_code_rsts(
+        self, pkg_name: str, pkg_path: Path, subdir: OptStr = None, max_depth: int = 4
+    ) -> list[str]:
         contents = []
         for path in pkg_path.iterdir():
             if path.is_dir():
@@ -355,9 +357,9 @@ def write_index(
         header: str,
         contents: Strings,
         *,
-        content_subdir: str = None,
-        subdir: str = None,
-        caption: str = None,
+        content_subdir: OptStr = None,
+        subdir: OptStr = None,
+        caption: OptStr = None,
         max_depth: int = 4,
         **kwargs,
     ):
@@ -379,7 +381,7 @@ def write_index(
         rendered = rst_toc_tree(header, content_fmt, contents, caption=caption, max_depth=max_depth, **kwargs)
         self.write_rst(name, rendered, subdir)
 
-    def write_rst(self, name: str, content: str, subdir: str = None):
+    def write_rst(self, name: str, content: str, subdir: OptStr = None):
         target_dir = self.output_dir.joinpath(subdir) if subdir else self.output_dir
         if not self.dry_run and not target_dir.exists():
             target_dir.mkdir(parents=True)
diff --git a/lib/cli_command_parser/formatting/commands.py b/lib/cli_command_parser/formatting/commands.py
index 43a8372b..57230031 100644
--- a/lib/cli_command_parser/formatting/commands.py
+++ b/lib/cli_command_parser/formatting/commands.py
@@ -24,7 +24,7 @@
     from ..core import CommandMeta
     from ..metadata import ProgramMetadata
     from ..parameters import BaseOption, BasePositional, Parameter, PassThru, SubCommand
-    from ..typing import Bool, CommandAny, CommandCls, CommandType
+    from ..typing import Bool, CommandAny, CommandCls, CommandType, OptStr
 
 __all__ = ['CommandHelpFormatter', 'get_formatter']
 
@@ -78,7 +78,7 @@ def _iter_params(self) -> Iterator[BasePositional | BaseOption | PassThru]:
         if params.pass_thru is not None:
             yield params.pass_thru
 
-    def _usage_parts(self, sub_cmd_choice: str = None, allow_sys_argv: Bool = True) -> Iterator[str]:
+    def _usage_parts(self, sub_cmd_choice: OptStr = None, allow_sys_argv: Bool = True) -> Iterator[str]:
         yield 'usage:'
         yield self._meta.get_prog(allow_sys_argv)
         if sub_cmd_choice:
@@ -91,7 +91,7 @@ def _usage_parts(self, sub_cmd_choice: str = None, allow_sys_argv: Bool = True)
     def format_usage(
         self,
         delim: str = ' ',
-        sub_cmd_choice: str = None,
+        sub_cmd_choice: OptStr = None,
         allow_sys_argv: Bool = True,
         cont_indent: int = 4,
     ) -> str:
@@ -149,7 +149,7 @@ def _format_rst(
     def _cmd_rst_lines(
         self,
         config: CommandConfig,
-        sub_cmd_choice: str = None,
+        sub_cmd_choice: OptStr = None,
         allow_sys_argv: Bool = False,
         include_epilog: Bool = False,
     ) -> Iterator[str]:
@@ -184,7 +184,7 @@ def _sub_cmds_rst_lines(
         config: CommandConfig,
         sub_command: SubCommand,
         level: int,
-        choice_base: str = None,
+        choice_base: OptStr = None,
         depth: int = 0,
         allow_sys_argv: Bool = False,
     ):
@@ -228,12 +228,15 @@ def get_formatter(command: CommandAny) -> CommandHelpFormatter:
 
 def get_usage_sub_cmds(command: CommandCls):
     cmd_mcs: Type[CommandMeta] = command.__class__  # Using metaclass to avoid potentially overwritten attrs
-    if not (parent := cmd_mcs.parent(command, False)):  # type: CommandType
+
+    parent: CommandMeta
+    if not (parent := cmd_mcs.parent(command, False)):
         return
 
     yield from get_usage_sub_cmds(parent)
 
-    if not (sub_cmd_param := cmd_mcs.params(parent).sub_command):  # type: SubCommand
+    sub_cmd_param: SubCommand
+    if not (sub_cmd_param := cmd_mcs.params(parent).sub_command):
         return
 
     try:
diff --git a/lib/cli_command_parser/formatting/params.py b/lib/cli_command_parser/formatting/params.py
index d3e0f17a..9e43624f 100644
--- a/lib/cli_command_parser/formatting/params.py
+++ b/lib/cli_command_parser/formatting/params.py
@@ -120,7 +120,7 @@ def iter_usage_parts(self, include_meta: Bool = False, full: Bool = False) -> It
         """Format the Parameter for use in the list of Parameters with their ``help='...'`` descriptions"""
         yield self.format_usage(include_meta=include_meta, full=full)
 
-    def format_description(self, rst: Bool = False, description: str = None) -> str:
+    def format_description(self, rst: Bool = False, description: OptStr = None) -> str:
         param = self.param
         if description is None:
             description = param.help or ''
@@ -170,7 +170,7 @@ def iter_usage_parts(self, include_meta: Bool = False, full: Bool = False) -> It
             metavar = self._format_usage_metavar()
             yield from (f'{opt} {metavar}' for opt in opts.option_strs())
 
-    def format_description(self, rst: Bool = False, description: str = None) -> str:
+    def format_description(self, rst: Bool = False, description: OptStr = None) -> str:
         description = super().format_description(rst, description)
         param: BaseOption = self.param
         if param.env_var and (param.show_env_var or (param.show_env_var is None and ctx.config.show_env_vars)):
@@ -436,7 +436,7 @@ def format_usage(self, include_meta: Bool = False, full: Bool = False, delim: st
         members = (mem.formatter.format_usage(include_meta, full, delim) for mem in self.param.members)
         return self.maybe_wrap_usage(self._get_choice_delim().join(members))
 
-    def format_description(self, rst: Bool = False, description: str = None) -> str:
+    def format_description(self, rst: Bool = False, description: OptStr = None) -> str:
         if description:
             return description
         group = self.param
diff --git a/lib/cli_command_parser/formatting/restructured_text.py b/lib/cli_command_parser/formatting/restructured_text.py
index bf849c1f..d0ca22bd 100644
--- a/lib/cli_command_parser/formatting/restructured_text.py
+++ b/lib/cli_command_parser/formatting/restructured_text.py
@@ -59,7 +59,7 @@ def spaced_rst_header(text: str, level: int = 1, before: bool = True) -> Iterato
 
 
 def _rst_directive(
-    directive: str, args: str = None, options: dict[str, Any] = None, indent: int = 4, check: Bool = False
+    directive: str, args: OptStr = None, options: dict[str, Any] | None = None, indent: int = 4, check: Bool = False
 ) -> Iterator[str]:
     yield f'.. {directive}:: {args}' if args else f'.. {directive}::'
     if options:
@@ -70,7 +70,7 @@ def _rst_directive(
 
 
 def rst_directive(
-    directive: str, args: str = None, options: dict[str, Any] = None, indent: int = 4, check: Bool = False
+    directive: str, args: OptStr = None, options: dict[str, Any] | None = None, indent: int = 4, check: Bool = False
 ) -> str:
     return '\n'.join(_rst_directive(directive, args, options, indent, check))
 
@@ -120,9 +120,9 @@ class RstTable:
 
     def __init__(
         self,
-        title: str = None,
-        subtitle: str = None,
-        headers: Sequence[str] = None,
+        title: OptStr = None,
+        subtitle: OptStr = None,
+        headers: Sequence[str] | None = None,
         *,
         show_title: Bool = True,
         use_table_directive: Bool = True,
@@ -138,7 +138,9 @@ def __init__(
             self.add_row(*headers, header=True)
 
     @classmethod
-    def from_dicts(cls, rows: RowMaps, columns: Sequence[T] = None, auto_headers: Bool = False, **kwargs) -> RstTable:
+    def from_dicts(
+        cls, rows: RowMaps, columns: Sequence[T] | None = None, auto_headers: Bool = False, **kwargs
+    ) -> RstTable:
         """
         Initialize a RstTable using the given keyword arguments, and populate its rows using the given dicts and
         :meth:`.add_dict_rows`.
@@ -168,7 +170,7 @@ def widths(self) -> tuple[int, ...]:
             self._updated = False
         return self._widths
 
-    def add_dict_rows(self, rows: RowMaps, columns: Sequence[T] = None, add_header: Bool = False):
+    def add_dict_rows(self, rows: RowMaps, columns: Sequence[T] | None = None, add_header: Bool = False):
         """Add a row for each dict in the given sequence of rows, where the keys represent the columns."""
         if not columns:
             columns = list(rows[0])
@@ -191,7 +193,7 @@ def _add_rows(self, rows: Iterable[Row]):
         self._rows.extend(rows)
         self._updated = True
 
-    def add_row(self, *columns: OptStr, index: int = None, header: bool = False):
+    def add_row(self, *columns: OptStr, index: int | None = None, header: bool = False):
         """
         Add a row to the table.
 
@@ -202,7 +204,7 @@ def add_row(self, *columns: OptStr, index: int = None, header: bool = False):
         """
         self._add_row(Row([Cell(c or '') for c in columns], header), index)
 
-    def _add_row(self, row: Row, index: int = None):
+    def _add_row(self, row: Row, index: int | None = None):
         if index is None:
             self._rows.append(row)
         else:
diff --git a/lib/cli_command_parser/inputs/choices.py b/lib/cli_command_parser/inputs/choices.py
index 076481e3..89f231be 100644
--- a/lib/cli_command_parser/inputs/choices.py
+++ b/lib/cli_command_parser/inputs/choices.py
@@ -59,7 +59,7 @@ def _normalize(self, value: str) -> T:
                 raise InvalidChoiceError(value, self.choices) from e
         return value
 
-    def _iter_normalized(self, value: Any, choices: Collection = None) -> Iterator[T]:
+    def _iter_normalized(self, value: Any, choices: Collection | None = None) -> Iterator[T]:
         yield value
         if not self.case_sensitive and (choices is None or isinstance(choices, (set, Mapping))):
             yield value.lower()
@@ -94,7 +94,7 @@ class Choices(_ChoicesBase[T]):
 
     __slots__ = ()
 
-    def __init__(self, choices: Collection[T], type: TypeFunc = None, case_sensitive: Bool = True):  # noqa
+    def __init__(self, choices: Collection[T], type: TypeFunc | None = None, case_sensitive: Bool = True):  # noqa
         if not case_sensitive and not all(isinstance(c, str) for c in choices):
             raise TypeError(f'Cannot combine case_sensitive=False with non-str {choices=}')
         elif isinstance(type, EnumChoices) and not any(isinstance(c, type.type) for c in choices):
diff --git a/lib/cli_command_parser/inputs/files.py b/lib/cli_command_parser/inputs/files.py
index 01bd2c3a..0dfc4f2f 100644
--- a/lib/cli_command_parser/inputs/files.py
+++ b/lib/cli_command_parser/inputs/files.py
@@ -10,7 +10,7 @@
 from abc import ABC
 from pathlib import Path as _Path
 
-from ..typing import FP, Bool, Converter, PathLike, T
+from ..typing import FP, Bool, Converter, OptStr, PathLike, T
 from .base import InputType
 from .exceptions import InputValidationError
 from .utils import FileWrapper, InputParam, StatMode, allows_write, fix_windows_path
@@ -143,8 +143,8 @@ def __init__(
         self,
         mode: str = 'r',
         *,
-        encoding: str = None,
-        errors: str = None,
+        encoding: OptStr = None,
+        errors: OptStr = None,
         lazy: Bool = True,
         parents: Bool = False,
         **kwargs,
diff --git a/lib/cli_command_parser/inputs/numeric.py b/lib/cli_command_parser/inputs/numeric.py
index 924720ea..314fa709 100644
--- a/lib/cli_command_parser/inputs/numeric.py
+++ b/lib/cli_command_parser/inputs/numeric.py
@@ -125,7 +125,7 @@ class NumRange(RangeMixin, _RangeInput[NT]):
 
     def __init__(
         self,
-        type: NumType = None,  # noqa
+        type: NumType | None = None,  # noqa
         snap: Bool = False,
         *,
         min: Number = None,  # noqa
diff --git a/lib/cli_command_parser/inputs/time.py b/lib/cli_command_parser/inputs/time.py
index 9568ea25..511b33f1 100644
--- a/lib/cli_command_parser/inputs/time.py
+++ b/lib/cli_command_parser/inputs/time.py
@@ -24,7 +24,7 @@
 from threading import RLock
 from typing import Collection, Iterator, Literal, Sequence, Type, TypeVar, overload
 
-from ..typing import Bool, Locale, Number, T, TimeBound
+from ..typing import Bool, Locale, Number, OptStr, T, TimeBound
 from ..utils import MissingMixin
 from .base import InputType, _FixedInputType
 from .exceptions import InputValidationError, InvalidChoiceError
@@ -75,10 +75,10 @@ def __exit__(self, exc_type, exc_val, exc_tb):
 
 class DTInput(_FixedInputType[T], ABC):
     __slots__ = ('locale',)
-    dt_type: str
+    dt_type: OptStr
     locale: Locale | None
 
-    def __init_subclass__(cls, dt_type: str = None, **kwargs):
+    def __init_subclass__(cls, dt_type: OptStr = None, **kwargs):
         """
         :param dt_type: Used in InvalidChoiceError / ValueError messages
         """
@@ -133,9 +133,9 @@ def __init__(
         full: Bool = True,
         abbreviation: Bool = True,
         numeric: Bool = False,
-        locale: Locale = None,
+        locale: Locale | None = None,
         out_format: str | DTFormatMode = DTFormatMode.FULL,
-        out_locale: Locale = None,
+        out_locale: Locale | None = None,
         fix_default: Bool = True,
     ):
         if not (full or abbreviation or numeric):
@@ -250,9 +250,9 @@ def __init__(
         abbreviation: Bool = True,
         numeric: Bool = False,
         iso: Bool = False,
-        locale: Locale = None,
+        locale: Locale | None = None,
         out_format: str | DTFormatMode = DTFormatMode.FULL,
-        out_locale: Locale = None,
+        out_locale: Locale | None = None,
         fix_default: Bool = True,
     ): ...
 
@@ -305,9 +305,9 @@ def __init__(
         full: Bool = True,
         abbreviation: Bool = True,
         numeric: Bool = True,
-        locale: Locale = None,
+        locale: Locale | None = None,
         out_format: str | DTFormatMode = DTFormatMode.FULL,
-        out_locale: Locale = None,
+        out_locale: Locale | None = None,
         fix_default: Bool = True,
     ): ...
 
@@ -408,7 +408,7 @@ def __init_subclass__(cls, type: Type[DT], **kwargs):  # noqa
     def __init__(
         self,
         formats: Collection[str],
-        locale: Locale = None,
+        locale: Locale | None = None,
         earliest: TimeBound = None,
         latest: TimeBound = None,
         fix_default: Bool = True,
@@ -513,7 +513,7 @@ class DateTime(DateTimeInput[datetime], type=datetime):
     def __init__(
         self,
         *formats: str,
-        locale: Locale = None,
+        locale: Locale | None = None,
         earliest: TimeBound = None,
         latest: TimeBound = None,
         fix_default: Bool = True,
@@ -539,7 +539,7 @@ class Date(DateTimeInput[date], type=date):
     def __init__(
         self,
         *formats: str,
-        locale: Locale = None,
+        locale: Locale | None = None,
         earliest: TimeBound = None,
         latest: TimeBound = None,
         fix_default: Bool = True,
@@ -565,7 +565,7 @@ class Time(DateTimeInput[time], type=time):
     def __init__(
         self,
         *formats: str,
-        locale: Locale = None,
+        locale: Locale | None = None,
         earliest: TimeBound = None,
         latest: TimeBound = None,
         fix_default: Bool = True,
@@ -586,7 +586,7 @@ def dt_repr(dt: datetime | date | time, use_repr: bool = True) -> str:
     return repr(dt_str) if use_repr else dt_str
 
 
-def normalize_dt(value: TimeBound, now: datetime = None) -> datetime | None:
+def normalize_dt(value: TimeBound, now: datetime | None = None) -> datetime | None:
     match value:
         case None | datetime():
             return value
diff --git a/lib/cli_command_parser/inputs/utils.py b/lib/cli_command_parser/inputs/utils.py
index 39d7ce58..b4868ffb 100644
--- a/lib/cli_command_parser/inputs/utils.py
+++ b/lib/cli_command_parser/inputs/utils.py
@@ -18,7 +18,7 @@
 from .exceptions import InputValidationError
 
 if TYPE_CHECKING:
-    from ..typing import FP, Bool, Converter, Number
+    from ..typing import FP, Bool, Converter, Number, OptStr
 
 __all__ = ['InputParam', 'StatMode', 'FileWrapper', 'fix_windows_path', 'range_str', 'RangeMixin']
 
@@ -46,7 +46,7 @@ def __set__(self, instance, value: Any):
 
 
 class StatMode(FixedFlag):
-    def __new__(cls, mode, friendly_name: str = None):
+    def __new__(cls, mode, friendly_name: OptStr = None):
         # Defined __new__ to avoid juggling dicts for the stat mode values and names
         obj = object.__new__(cls)
         if friendly_name:
@@ -90,9 +90,9 @@ def __init__(
         self,
         path: Path,
         mode: str = 'r',
-        encoding: str = None,
-        errors: str = None,
-        converter: Converter = None,
+        encoding: OptStr = None,
+        errors: OptStr = None,
+        converter: Converter | None = None,
         pass_file: Bool = False,
         parents: Bool = False,
     ):
diff --git a/lib/cli_command_parser/parameters/actions.py b/lib/cli_command_parser/parameters/actions.py
index 318d4379..7c16a121 100644
--- a/lib/cli_command_parser/parameters/actions.py
+++ b/lib/cli_command_parser/parameters/actions.py
@@ -16,7 +16,7 @@
 
 if TYPE_CHECKING:
     from .base import Parameter  # noqa
-    from ..typing import Bool, CommandObj, T_co
+    from ..typing import Bool, CommandObj, OptStr
 
 __all__ = [
     'ParamAction',
@@ -44,7 +44,9 @@ class ParamAction(ABC, Generic[Param]):
     accepts_values: bool = False
     accepts_consts: bool = False
 
-    def __init_subclass__(cls, default=_PANotSet, accepts_values: bool = None, accepts_consts: bool = None, **kwargs):
+    def __init_subclass__(
+        cls, default=_PANotSet, accepts_values: bool | None = None, accepts_consts: bool | None = None, **kwargs
+    ):
         super().__init_subclass__(**kwargs)
         cls.name = camel_to_snake_case(cls.__name__)
         if default is not _PANotSet:
@@ -72,7 +74,7 @@ def default_nargs(self) -> Nargs:
     # region Add Parsed Value / Constant Methods
 
     @abstractmethod
-    def add_value(self, value: str, *, combo: bool = False, joined: bool = False, env_var: str = None) -> Found:
+    def add_value(self, value: str, *, combo: bool = False, joined: bool = False, env_var: OptStr = None) -> Found:
         """
         Execute this action for the given Parameter and value.
 
@@ -96,7 +98,7 @@ def add_env_value(self, value: str, env_var: str) -> Found:
     #         added += self.add_value(value, combo=combo)
     #     return added
 
-    def add_const(self, *, opt: str = None, combo: bool = False) -> Found:  # noqa
+    def add_const(self, *, opt: OptStr = None, combo: bool = False) -> Found:  # noqa
         ctx.record_action(self.param)
         raise MissingArgument(self.param)
 
@@ -261,7 +263,7 @@ class Store(ValueMixin, ParamAction, default=None, accepts_values=True):
 
     # region Add Parsed Value / Constant Methods
 
-    def add_value(self, value: str, *, combo: bool = False, joined: Bool = False, env_var: str = None) -> Found:
+    def add_value(self, value: str, *, combo: bool = False, joined: Bool = False, env_var: OptStr = None) -> Found:
         ctx.record_action(self.param)
         value = self.param.prepare_value(value, combo, env_var)
         self.param.validate(value, joined)
@@ -297,7 +299,7 @@ class Append(ValueMixin, ParamAction, accepts_values=True):
 
     # region Add Parsed Value / Constant Methods
 
-    def add_value(self, value: str, *, combo: bool = False, joined: Bool = False, env_var: str = None) -> Found:
+    def add_value(self, value: str, *, combo: bool = False, joined: Bool = False, env_var: OptStr = None) -> Found:
         ctx.record_action(self.param)
         value = self.param.prepare_value(value, combo, env_var)
         self.param.validate(value)
@@ -392,7 +394,7 @@ class BasicConstAction(ConstMixin, ParamAction, ABC, accepts_consts=True):
 
     # region Add Parsed Value / Constant Methods
 
-    def add_value(self, value: str, *, combo: bool = False, joined: Bool = False, env_var: str = None) -> Found:  # noqa
+    def add_value(self, value: str, *, combo: bool = False, joined: Bool = False, env_var: OptStr = None) -> Found:  # noqa
         ctx.record_action(self.param)
         raise BadArgument(self.param, f'does not accept values, but {value=} was provided')
 
@@ -414,7 +416,7 @@ class StoreConst(BasicConstAction, default=None):
 
     # region Add Parsed Value / Constant Methods
 
-    def add_const(self, *, opt: str = None, combo: bool = False) -> Found:
+    def add_const(self, *, opt: OptStr = None, combo: bool = False) -> Found:
         ctx.record_action(self.param)
         self.set_const(self.param.get_const(opt))
         return 1
@@ -427,7 +429,7 @@ class AppendConst(BasicConstAction, append=True):
 
     # region Add Parsed Value / Constant Methods
 
-    def add_const(self, *, opt: str = None, combo: bool = False) -> Found:
+    def add_const(self, *, opt: OptStr = None, combo: bool = False) -> Found:
         ctx.record_action(self.param)
         # TODO: Fix nargs consistency for overall vs per-arg
         self.append_const(self.param.get_const(opt))
@@ -447,7 +449,7 @@ def get_default(self, command: CommandObj | None = None, missing_default=_NotSet
 #     __slots__ = ()
 #     default_nargs = Nargs('?')
 #
-#     def add_const(self, *, opt: str = None, combo: bool = False) -> Found:
+#     def add_const(self, *, opt: OptStr = None, combo: bool = False) -> Found:
 #         ctx.record_action(self.param)
 #         self.set_const(self.param.get_const(opt))
 #         return 1
@@ -457,7 +459,7 @@ def get_default(self, command: CommandObj | None = None, missing_default=_NotSet
 #     __slots__ = ()
 #     default_nargs = Nargs('?')
 #
-#     def add_const(self, *, opt: str = None, combo: bool = False) -> Found:
+#     def add_const(self, *, opt: OptStr = None, combo: bool = False) -> Found:
 #         ctx.record_action(self.param)
 #         self.append_const(self.param.get_const(opt))
 #         return 1
@@ -476,12 +478,12 @@ def _add(self, value: int):
 
     # region Add Parsed Value / Constant Methods
 
-    def add_const(self, *, opt: str = None, combo: bool = False) -> Found:
+    def add_const(self, *, opt: OptStr = None, combo: bool = False) -> Found:
         ctx.record_action(self.param)
         self._add(self.param.get_const(opt))
         return 1
 
-    def add_value(self, value: str, *, combo: bool = False, joined: Bool = False, env_var: str = None) -> Found:
+    def add_value(self, value: str, *, combo: bool = False, joined: Bool = False, env_var: OptStr = None) -> Found:
         ctx.record_action(self.param)
         value = self.param.prepare_value(value, combo, env_var)
         self.param.validate(value, joined)
@@ -496,7 +498,7 @@ class Concatenate(Append):
 
     # region Add Parsed Value / Constant Methods
 
-    def add_value(self, value: str, *, combo: bool = False, joined: Bool = False, env_var: str = None) -> Found:
+    def add_value(self, value: str, *, combo: bool = False, joined: Bool = False, env_var: OptStr = None) -> Found:
         param = self.param
         values = value.split()
         if not param.is_valid_arg(' '.join(values)):
diff --git a/lib/cli_command_parser/parameters/base.py b/lib/cli_command_parser/parameters/base.py
index 3f7cac02..041c02f0 100644
--- a/lib/cli_command_parser/parameters/base.py
+++ b/lib/cli_command_parser/parameters/base.py
@@ -33,6 +33,7 @@
 from .option_strings import OptionStrings
 
 if TYPE_CHECKING:
+    from ..core import CommandMeta
     from ..formatting.params import ParamHelpFormatter
     from ..typing import Bool, CommandAny, CommandCls, CommandObj, LeadingDash, OptStr, OptStrs, Strings
     from .actions import ParamAction
@@ -58,22 +59,22 @@ class ParamBase(ABC):
 
     # fmt: off
     # Class Attributes
-    missing_hint: str = None        #: Hint to provide if this param/group is missing
+    missing_hint: OptStr = None         #: Hint to provide if this param/group is missing
     # Instance Attributes
-    _attr_name: str = None          #: Always the name of the attr that points to this object
-    _name: str = None               #: An explicitly provided name, or the name of the attr that points to this object
-    group: ParamGroup = None        #: The group this object is a member of, if any
-    command: CommandCls = None      #: The :class:`.Command` this object is a member of
-    required: Bool                  #: Whether this param/group is required
-    help: str                       #: The description for this param/group that will appear in ``--help`` text
-    hide: Bool                      #: Whether this param/group should be hidden in ``--help`` text
+    _attr_name: OptStr = None           #: Always the name of the attr that points to this object
+    _name: OptStr = None                #: An explicitly provided name, or the name of the attr that points to this obj
+    group: ParamGroup | None = None     #: The group this object is a member of, if any
+    command: CommandMeta | None = None  #: The :class:`.Command` this object is a member of
+    required: Bool                      #: Whether this param/group is required
+    help: str                           #: The description for this param/group that will appear in ``--help`` text
+    hide: Bool                          #: Whether this param/group should be hidden in ``--help`` text
     # fmt: on
 
     def __init__(
         self,
-        name: str | None = None,
+        name: OptStr = None,
         required: Bool = False,
-        help: str | None = None,  # noqa
+        help: OptStr = None,  # noqa
         hide: Bool = False,
     ):
         self.__doc__ = help  # Prevent this class's docstring from showing up for params in generated documentation
@@ -94,7 +95,7 @@ def name(self) -> str:
         return self._default_name()
 
     @name.setter
-    def name(self, value: str | None):
+    def name(self, value: OptStr):
         if value is not None:
             self._name = value
 
@@ -202,7 +203,7 @@ class Parameter(ParamBase, Generic[T_co], ABC):
     _action_map: dict[str, Type[ParamAction]] = {}
     _repr_attrs: Strings | None = None                                  #: Attributes to include in ``repr()`` output
     # Instance attributes with class defaults
-    metavar: str = None
+    metavar: OptStr = None
     nargs: Nargs                                                        # Expected to be set in subclasses
     type: Callable[[str], T_co] | None = None                           # Expected to be set in subclasses
     allow_leading_dash: AllowLeadingDash = AllowLeadingDash.NUMERIC     # Set in some subclasses
@@ -231,13 +232,13 @@ def __init__(  # pylint: disable=R0913
         self,
         action: str,
         *,
-        help: str | None = None,  # noqa
+        help: OptStr = None,  # noqa
         hide: Bool = False,
-        metavar: str | None = None,
-        name: str | None = None,
+        metavar: OptStr = None,
+        name: OptStr = None,
         required: Bool = False,
         default: Any = _NotSet,
-        default_cb: DefaultFunc = None,
+        default_cb: DefaultFunc | None = None,
         cb_with_cmd: Bool = False,
         show_default: Bool = None,
         strict_default: Bool = False,
@@ -348,7 +349,7 @@ def get_const(self, opt_str: OptStr = None):
     def get_env_const(self, value: str, env_var: str) -> tuple[T_co, bool]:
         return _NotSet, False
 
-    def prepare_value(self, value: str, short_combo: Bool = False, env_var: str = None) -> T_co:
+    def prepare_value(self, value: str, short_combo: Bool = False, env_var: OptStr = None) -> T_co:
         if self.type is None:
             return value
         try:
@@ -463,7 +464,7 @@ class BasePositional(Parameter[T_co], ABC):
 
     _default_ok: bool = False
 
-    def __init_subclass__(cls, default_ok: bool = None, **kwargs):  # pylint: disable=W0222
+    def __init_subclass__(cls, default_ok: bool | None = None, **kwargs):  # pylint: disable=W0222
         """
         :param default_ok: Whether default values are supported for this Parameter type
         :param kwargs: Additional keyword arguments to pass to :meth:`.Parameter.__init_subclass__`.
@@ -529,7 +530,7 @@ def __init__(
         self,
         *option_strs: str,
         action: str,
-        name_mode: OptionNameMode | str | None = _NotSet,
+        name_mode: OptionNameMode | OptStr = _NotSet,
         env_var: OptStrs = None,
         strict_env: bool = True,
         use_env_value: Bool = None,
diff --git a/lib/cli_command_parser/parameters/choice_map.py b/lib/cli_command_parser/parameters/choice_map.py
index ecad4fad..41f38b9a 100644
--- a/lib/cli_command_parser/parameters/choice_map.py
+++ b/lib/cli_command_parser/parameters/choice_map.py
@@ -96,7 +96,7 @@ class ChoiceMap(BasePositional[str], Generic[T], actions=(Concatenate,)):
     formatter: ChoiceMapHelpFormatter
 
     def __init_subclass__(  # pylint: disable=W0222
-        cls, title: str = None, choice_validation_exc: Type[Exception] = None, **kwargs
+        cls, title: OptStr = None, choice_validation_exc: Type[Exception] = None, **kwargs
     ):
         """
         :param title: Default title to use for help text sections containing the choices for this parameter.
@@ -109,7 +109,7 @@ def __init_subclass__(  # pylint: disable=W0222
         if choice_validation_exc is not None:
             cls._choice_validation_exc = choice_validation_exc
 
-    def __init__(self, *, action: str = 'concatenate', title: str = None, description: str = None, **kwargs):
+    def __init__(self, *, action: str = 'concatenate', title: OptStr = None, description: OptStr = None, **kwargs):
         super().__init__(action=action, **kwargs)
         self.title = title
         self.description = description
@@ -143,15 +143,15 @@ def _validate_positional(cls, value: str):
         if bad := {c for c in value if (c in whitespace and c != ' ') or c not in printable}:
             raise cls._choice_validation_exc(f'Invalid {cls.__name__} choice={value!r} - invalid characters: {bad}')
 
-    def register_choice(self, choice: str, target: T = _NotSet, help: str = None):  # noqa
+    def register_choice(self, choice: str, target: T = _NotSet, help: OptStr = None):  # noqa
         self._validate_positional(choice)
         self._register_choice(choice, target, help)
 
     def _register_choice(
         self,
         choice: OptStr,
-        target: T | None = _NotSet,
-        help: str = None,  # noqa
+        target: T | None | _NotSetType = _NotSet,
+        help: OptStr = None,  # noqa
         local: bool = False,
     ):
         try:
@@ -223,7 +223,7 @@ def __init__(
         self,
         *,
         required: Bool = True,
-        default_help: str = None,
+        default_help: OptStr = None,
         local_choices: Mapping[str, str] | Collection[str] | None = None,
         **kwargs,
     ):
@@ -288,8 +288,8 @@ def register(
         self,
         command_or_choice: str | CommandCls | None = None,
         *,
-        choice: str = None,
-        help: str = None,  # noqa
+        choice: OptStr = None,
+        help: OptStr = None,  # noqa
     ) -> Callable[[CommandCls], CommandCls]:
         """
         Class decorator version of :meth:`.register_command`.  Registers the wrapped :class:`.Command` as the
@@ -336,7 +336,7 @@ def register_action(
         self,
         choice: OptStr,
         method: MethodType,
-        help: str = None,  # noqa
+        help: OptStr = None,  # noqa
         default: Bool = False,
     ) -> MethodType:
         if help is None:
@@ -362,8 +362,8 @@ def register(
         self,
         method_or_choice: str | MethodType | None = None,
         *,
-        choice: str = None,
-        help: str = None,  # noqa
+        choice: OptStr = None,
+        help: OptStr = None,  # noqa
         default: Bool = False,
     ) -> MethodType | Callable[[MethodType], MethodType]:
         """
diff --git a/lib/cli_command_parser/parameters/options.py b/lib/cli_command_parser/parameters/options.py
index 5e94f275..bd5488ea 100644
--- a/lib/cli_command_parser/parameters/options.py
+++ b/lib/cli_command_parser/parameters/options.py
@@ -77,13 +77,13 @@ class Option(BaseOption[T_co | TD], actions=(Store, Append)):
     def __init__(
         self,
         *option_strs: str,
-        nargs: NargsValue = None,
-        action: Literal['store', 'append'] = None,
+        nargs: NargsValue | None = None,
+        action: Literal['store', 'append'] | None = None,
         default: TD = _NotSet,
         required: Bool = False,
         type: InputTypeFunc = None,  # noqa
         choices: ChoicesType = None,
-        allow_leading_dash: LeadingDash = None,
+        allow_leading_dash: LeadingDash | None = None,
         **kwargs,
     ):
         if nargs_provided := nargs is not None:
@@ -162,7 +162,7 @@ def __init__(
         default: TD = _NotSet,
         default_cb=_NotSet,
         const: TC = _NotSet,
-        type: TypeFunc = None,  # noqa
+        type: TypeFunc | None = None,  # noqa
         **kwargs,
     ):
         if const is _NotSet:
@@ -246,14 +246,14 @@ def __init__(
         self,
         *option_strs: str,
         consts: tuple[TC, TA] = (True, False),
-        alt_prefix: str = None,
-        alt_long: str = None,
-        alt_short: str = None,
-        alt_help: str = None,
+        alt_prefix: OptStr = None,
+        alt_long: OptStr = None,
+        alt_short: OptStr = None,
+        alt_help: OptStr = None,
         action: ConstAct = 'store_const',
         default: TD = _NotSet,
-        default_cb: Callable[[], TD] = None,
-        type: TypeFunc = None,  # noqa
+        default_cb: Callable[[], TD] | None = None,
+        type: TypeFunc | None = None,  # noqa
         **kwargs,
     ):
         if alt_short and '-' in alt_short[1:]:
@@ -342,7 +342,7 @@ def __init__(
         self,
         *option_strs: str,
         order: int | float = 1,
-        func: Callable = None,
+        func: Callable | None = None,
         before_main: Bool = True,  # noqa  # pylint: disable=W0621
         always_available: Bool = False,
         **kwargs,
@@ -423,12 +423,12 @@ def __reduce__(self):
 action_flag = ActionFlag  # pylint: disable=C0103
 
 
-def before_main(*option_strs: str, order: int | float = 1, func: Callable = None, **kwargs) -> ActionFlag:
+def before_main(*option_strs: str, order: int | float = 1, func: Callable | None = None, **kwargs) -> ActionFlag:
     """An ActionFlag that will be executed before :meth:`.Command.main`"""
     return ActionFlag(*option_strs, order=order, func=func, before_main=True, **kwargs)
 
 
-def after_main(*option_strs: str, order: int | float = 1, func: Callable = None, **kwargs) -> ActionFlag:
+def after_main(*option_strs: str, order: int | float = 1, func: Callable | None = None, **kwargs) -> ActionFlag:
     """An ActionFlag that will be executed after :meth:`.Command.main`"""
     return ActionFlag(*option_strs, order=order, func=func, before_main=False, **kwargs)
 
@@ -477,7 +477,7 @@ def __init__(
         init: int = 0,
         const: int = 1,
         default: int = _NotSet,
-        default_cb: Callable[[], int] = None,
+        default_cb: Callable[[], int] | None = None,
         required: bool = False,
         **kwargs,
     ):
@@ -499,7 +499,7 @@ def register_default_cb(self, method: CommandMethod) -> CommandMethod:
             self.default_cb = None
         return super().register_default_cb(method)
 
-    def prepare_value(self, value: str | None, short_combo: bool = False, env_var: str = None) -> int:
+    def prepare_value(self, value: str | None, short_combo: bool = False, env_var: OptStr = None) -> int:
         try:
             return self.type(value)
         except (ValueError, TypeError) as e:
diff --git a/lib/cli_command_parser/parameters/positionals.py b/lib/cli_command_parser/parameters/positionals.py
index e525bd8d..76b7b0df 100644
--- a/lib/cli_command_parser/parameters/positionals.py
+++ b/lib/cli_command_parser/parameters/positionals.py
@@ -54,14 +54,14 @@ class Positional(BasePositional, default_ok=True, actions=(Store, Append)):
 
     def __init__(
         self,
-        nargs: NargsValue = None,
-        action: Literal['store', 'append'] = None,
+        nargs: NargsValue | None = None,
+        action: Literal['store', 'append'] | None = None,
         type: InputTypeFunc = None,  # noqa
         default: Any = _NotSet,
         *,
-        default_cb: DefaultFunc = None,
+        default_cb: DefaultFunc | None = None,
         choices: ChoicesType = None,
-        allow_leading_dash: LeadingDash = None,
+        allow_leading_dash: LeadingDash | None = None,
         **kwargs,
     ):
         if nargs_provided := nargs is not None:
diff --git a/lib/cli_command_parser/testing.py b/lib/cli_command_parser/testing.py
index 844dd09c..58c86ed0 100644
--- a/lib/cli_command_parser/testing.py
+++ b/lib/cli_command_parser/testing.py
@@ -91,34 +91,34 @@ class ParserTest(TestCase):
     #     print()
     #     return super().subTest(*args, **kwargs)
 
-    def assert_dict_equal(self, d1, d2, msg: str = None):
+    def assert_dict_equal(self, d1, d2, msg: OptStr = None):
         self.assertIsInstance(d1, dict, 'First argument is not a dictionary')
         self.assertIsInstance(d2, dict, 'Second argument is not a dictionary')
         if d1 != d2:
             self.fail(self._formatMessage(msg, f'{d1} != {d2}\n{format_dict_diff(d1, d2)}'))
 
-    def assert_raises_contains_str(self, expected_exc: Type[BaseException], expected_text: str, msg: str = None):
+    def assert_raises_contains_str(self, expected_exc: Type[BaseException], expected_text: str, msg: OptStr = None):
         return AssertRaisesWithStringContext(self, expected_exc, expected_text, msg)
 
-    def assert_parse_results(self, cmd_cls: CommandCls, argv: Argv, expected: Expected, msg: str = None) -> Command:
+    def assert_parse_results(self, cmd_cls: CommandCls, argv: Argv, expected: Expected, msg: OptStr = None) -> Command:
         cmd = cmd_cls.parse(argv)
         parsed = cmd.ctx.get_parsed(cmd, exclude=EXCLUDE_ACTIONS)
         if expected != parsed:
             self.fail(msg or f'Expected results ({expected}) != {parsed=}\n{format_dict_diff(expected, parsed)}')
         return cmd
 
-    def assert_parse_results_cases(self, cmd_cls: CommandCls, cases: Iterable[Case], msg: str = None):
+    def assert_parse_results_cases(self, cmd_cls: CommandCls, cases: Iterable[Case], msg: OptStr = None):
         for argv, expected in cases:
             with self.subTest(expected='results', argv=argv):
                 self.assert_parse_results(cmd_cls, argv, expected, msg)
 
     def assert_env_parse_results(
-        self, cmd_cls: CommandCls, argv: Argv, env: Env, expected: Expected, msg: str = None
+        self, cmd_cls: CommandCls, argv: Argv, env: Env, expected: Expected, msg: OptStr = None
     ) -> Command:
         with patch(OPT_ENV_MOD, env):
             return self.assert_parse_results(cmd_cls, argv, expected, msg)
 
-    def assert_env_parse_results_cases(self, cmd_cls: CommandCls, cases: Iterable[EnvCase], msg: str = None):
+    def assert_env_parse_results_cases(self, cmd_cls: CommandCls, cases: Iterable[EnvCase], msg: OptStr = None):
         for argv, env, expected in cases:
             with self.subTest(expected='results', argv=argv, env=env):
                 self.assert_env_parse_results(cmd_cls, argv, env, expected, msg)
@@ -128,8 +128,8 @@ def assert_parse_fails(
         cmd_cls: CommandCls,
         argv: Argv,
         expected_exc: ExcType = UsageError,
-        expected_pattern: str = None,
-        msg: str = None,
+        expected_pattern: OptStr = None,
+        msg: OptStr = None,
         regex: bool = False,
     ):
         if expected_pattern and regex:
@@ -139,14 +139,14 @@ def assert_parse_fails(
             with AssertRaisesWithStringContext(self, expected_exc, expected_pattern, msg):
                 cmd_cls.parse(argv)
 
-    def assert_parse_fails_cases(self, cmd_cls: CommandCls, cases: ExcCases, exc: ExcType = None, msg: str = None):
+    def assert_parse_fails_cases(self, cmd_cls: CommandCls, cases: ExcCases, exc: ExcType = None, msg: OptStr = None):
         for argv, exc, pat in _iter_exc_cases(cases, exc):
             with self.subTest(expected='exception', argv=argv):
                 with AssertRaisesWithStringContext(self, exc, pat, msg):
                     cmd_cls.parse(argv)
 
     def assert_argv_parse_fails_cases(
-        self, cmd_cls: CommandCls, cases: Iterable[Argv], exc: ExcType = UsageError, msg: str = None
+        self, cmd_cls: CommandCls, cases: Iterable[Argv], exc: ExcType = UsageError, msg: OptStr = None
     ):
         """Convenience method for calling :meth:`.assert_parse_fails_cases` with a default exception type."""
         self.assert_parse_fails_cases(cmd_cls, cases, exc, msg)
@@ -156,20 +156,20 @@ def assert_call_fails(
         func: Callable,
         kwargs: Kwargs,
         exc: ExcType = Exception,
-        expected_exc_msg: str = None,
-        msg: str = None,
+        expected_exc_msg: OptStr = None,
+        msg: OptStr = None,
     ):
         with AssertRaisesWithStringContext(self, exc, expected_exc_msg, msg):
             func(**kwargs)
 
-    def assert_call_fails_cases(self, func: Callable, cases: Iterable[CallExceptionCase], msg: str = None):
+    def assert_call_fails_cases(self, func: Callable, cases: Iterable[CallExceptionCase], msg: OptStr = None):
         for kwargs, exc, pat in _iter_exc_cases(cases):
             with self.subTest(expected='exception', kwargs=kwargs):
                 with AssertRaisesWithStringContext(self, exc, pat, msg):
                     func(**kwargs)
 
     def assert_strings_equal(
-        self, expected: str, actual: str, message: str = None, diff_lines: int = 3, trim: bool = False
+        self, expected: str, actual: str, message: OptStr = None, diff_lines: int = 3, trim: bool = False
     ):
         if trim:
             expected = expected.rstrip()
@@ -198,7 +198,7 @@ def env_vars(self, case: str, **env_vars):
             yield
 
 
-def _iter_exc_cases(cases: ExcCases | CallExceptionCases, exc: ExcType = None):
+def _iter_exc_cases(cases: ExcCases | CallExceptionCases, exc: ExcType | None = None):
     if exc is not None:
         for args in cases:
             yield args, exc, None
diff --git a/lib/cli_command_parser/typing.py b/lib/cli_command_parser/typing.py
index 993d7903..beaf9cfe 100644
--- a/lib/cli_command_parser/typing.py
+++ b/lib/cli_command_parser/typing.py
@@ -18,7 +18,6 @@
     Pattern,
     Sequence,
     TextIO,
-    Tuple,
     Type,
     TypeVar,
     Union,
@@ -57,7 +56,7 @@
 Strings = Collection[str]
 PathLike = Union[str, 'Path']
 
-Locale = Union[str, Tuple[Union[str, None], Union[str, None]]]
+Locale = str | tuple[OptStr, OptStr]
 TimeBound = Union['datetime', 'date', 'time', 'timedelta', None]
 
 FP = Union[TextIO, BinaryIO]
diff --git a/tests/test_conversion/test_convert_argparse.py b/tests/test_conversion/test_convert_argparse.py
index 1230ee25..a08a3268 100755
--- a/tests/test_conversion/test_convert_argparse.py
+++ b/tests/test_conversion/test_convert_argparse.py
@@ -64,7 +64,9 @@ def prep_cmd(*members: str, name: str = CMD0, base: str = 'Command', suffix: str
     return cls_def_line
 
 
-def prep_group(*add_args: str, title: str = None, description: str = None, parser: str = 'p', var: str = 'g') -> str:
+def prep_group(
+    *add_args: str, title: str | None = None, description: str | None = None, parser: str = 'p', var: str = 'g'
+) -> str:
     group_arg_str = ', '.join(f'{k}={v!r}' for k, v in {'title': title, 'description': description}.items() if v)
     add_arg_iter = (f'{var}.add_argument({arg})' for arg in add_args)
     return '\n'.join((f'{var} = {parser}.add_argument_group({group_arg_str})', *add_arg_iter))
diff --git a/tests/test_documentation/test_help_text.py b/tests/test_documentation/test_help_text.py
index 15717109..a44092a2 100755
--- a/tests/test_documentation/test_help_text.py
+++ b/tests/test_documentation/test_help_text.py
@@ -493,9 +493,9 @@ def assert_help_and_rst_match(
         mode: str,
         param_help_map: dict[str, str],
         help_header: str,
-        cmd_mode: str = None,
-        sc_kwargs: dict[str, Any] = None,
-        cmd_kwargs: dict[str, Any] = None,
+        cmd_mode: str | None = None,
+        sc_kwargs: dict[str, Any] | None = None,
+        cmd_kwargs: dict[str, Any] | None = None,
     ) -> Iterator[CommandCls]:
         if not cmd_kwargs:
             cmd_kwargs = {}
@@ -674,7 +674,9 @@ def prep_expected_rst(table_fmt_str: str, param_help_map: dict[str, str]) -> str
 
 
 class ShowDefaultsTest(TestCase):
-    def assert_default_x_in_help_text(self, defaults: Iterable[Any], expect_in: bool, check_str: str = None, **kwargs):
+    def assert_default_x_in_help_text(
+        self, defaults: Iterable[Any], expect_in: bool, check_str: str | None = None, **kwargs
+    ):
         for default in defaults:
             with self.subTest(default=default, expect_in=expect_in):
                 default_str = check_str or f'(default: {default!r})'
diff --git a/tests/test_documentation/test_user_docs.py b/tests/test_documentation/test_user_docs.py
index cd0f3d5e..831288bc 100755
--- a/tests/test_documentation/test_user_docs.py
+++ b/tests/test_documentation/test_user_docs.py
@@ -3,7 +3,7 @@
 import re
 from inspect import Signature
 from pathlib import Path
-from typing import Callable, Collection, Dict, Set
+from typing import Callable, Collection
 from unittest import TestCase, main
 
 from cli_command_parser.config import CommandConfig
@@ -12,7 +12,7 @@
 DOCS_SRC = Path(__file__).resolve().parents[2].joinpath('docs', '_src')
 
 
-def get_doc_params(rst_name: str, section_start: str, section_end: str = None) -> Dict[str, str]:
+def get_doc_params(rst_name: str, section_start: str, section_end: str | None = None) -> dict[str, str]:
     data = DOCS_SRC.joinpath(rst_name).read_text('utf-8')
     start = data.index(section_start)
     if section_end:
@@ -44,7 +44,7 @@ def get_doc_params(rst_name: str, section_start: str, section_end: str = None) -
     return params
 
 
-def get_func_params(func: Callable, skip: Collection[str] = None) -> Set[str]:
+def get_func_params(func: Callable, skip: Collection[str] | None = None) -> set[str]:
     sig = Signature.from_callable(func)
     params = set(sig.parameters)
     if skip:
diff --git a/tests/test_examples/test_examples_via_subprocess.py b/tests/test_examples/test_examples_via_subprocess.py
index 61ba029d..201f962e 100755
--- a/tests/test_examples/test_examples_via_subprocess.py
+++ b/tests/test_examples/test_examples_via_subprocess.py
@@ -5,7 +5,6 @@
 from operator import xor
 from pathlib import Path
 from subprocess import PIPE, Popen
-from typing import Tuple
 from unittest import TestCase, TestSuite as _TestSuite, main
 
 EXAMPLES_DIR = Path(__file__).resolve().parents[2].joinpath('examples')
@@ -57,13 +56,13 @@ def __eq__(self, other):
 
 
 class ExampleScriptTest(TestCase):
-    _path: str = None
+    _path: str | None = None
 
     def __init_subclass__(cls, file: str, **kwargs):  # noqa
         super().__init_subclass__(**kwargs)
         cls._path = EXAMPLES_DIR.joinpath(file).as_posix()
 
-    def call_script(self, *args) -> Tuple[int, str, str]:
+    def call_script(self, *args) -> tuple[int, str, str]:
         proc = Popen([sys.executable, self._path, *args], text=True, stdout=PIPE, stderr=PIPE)
         stdout = proc.stdout.read()
         proc.stdout.close()
diff --git a/tests/test_inputs/test_file_inputs.py b/tests/test_inputs/test_file_inputs.py
index 902d8db6..9fb45355 100755
--- a/tests/test_inputs/test_file_inputs.py
+++ b/tests/test_inputs/test_file_inputs.py
@@ -36,7 +36,7 @@ def temp_chdir(path: Path):
 
 
 @contextmanager
-def temp_path(file: str = None, touch: bool = False) -> Iterator[Path]:
+def temp_path(file: str | None = None, touch: bool = False) -> Iterator[Path]:
     with TemporaryDirectory() as tmp_dir:
         d = Path(tmp_dir)
         if file: