diff --git a/src/linktools/__main__.py b/src/linktools/__main__.py
index c88c0fe3..35a5c415 100644
--- a/src/linktools/__main__.py
+++ b/src/linktools/__main__.py
@@ -33,6 +33,7 @@
 from rich import get_console
 from rich.tree import Tree
 
+from linktools.cli.argparse import add_subparsers
 from ._environ import environ
 from .cli import BaseCommand, walk_commands
 from .decorator import cached_property
@@ -91,13 +92,13 @@ def command_infos(self) -> Dict[CategoryInfo, List[CommandInfo]]:
         return command_infos
 
     def init_arguments(self, parser: ArgumentParser) -> None:
-        catalog_parsers = parser.add_subparsers(metavar="CATALOG", required=True)
+        catalog_parsers = add_subparsers(parser, metavar="CATALOG", required=True)
         for category_info, command_infos in self.command_infos.items():
             catalog_parser = catalog_parsers.add_parser(
                 category_info.name,
                 help=category_info.description
             )
-            command_parsers = catalog_parser.add_subparsers(metavar="COMMAND", required=True)
+            command_parsers = add_subparsers(catalog_parser, metavar="COMMAND", required=True)
             for command_info in command_infos:
                 command_parser = command_info.command.create_argument_parser(
                     command_info.name,
diff --git a/src/linktools/cli/__init__.py b/src/linktools/cli/__init__.py
index 9708bfd9..90fdf07f 100644
--- a/src/linktools/cli/__init__.py
+++ b/src/linktools/cli/__init__.py
@@ -27,6 +27,8 @@
  /_==__==========__==_ooo__ooo=_/'   /___________,"
 """
 
+from . import argparse
+
 from .command import \
     LogCommandMixin, \
     BaseCommand, CommandError, \
diff --git a/src/linktools/cli/argparse.py b/src/linktools/cli/argparse.py
index 17d2a20f..0bfaa40f 100644
--- a/src/linktools/cli/argparse.py
+++ b/src/linktools/cli/argparse.py
@@ -122,3 +122,9 @@ def wrapper(o):
         raise ValueError("value not in range %s-%s" % (min, max))
 
     return wrapper
+
+
+def add_subparsers(parser: argparse.ArgumentParser, **kwargs):
+    if sys.version_info < (3, 7):
+        kwargs.pop("required", None)
+    return parser.add_subparsers(**kwargs)
diff --git a/src/linktools/cli/command.py b/src/linktools/cli/command.py
index 6388c2ab..8902ac0c 100644
--- a/src/linktools/cli/command.py
+++ b/src/linktools/cli/command.py
@@ -42,7 +42,7 @@
 import rich
 from rich import get_console
 
-from .argparse import BooleanOptionalAction
+from .argparse import BooleanOptionalAction, add_subparsers
 from .._environ import BaseEnviron, environ
 from .._logging import LogHandler
 from ..decorator import cached_property
@@ -275,7 +275,7 @@ def add_subcommands(self: "BaseCommand", parser: ArgumentParser = None, target:
         parser = parser or self._argument_parser
         target = target or self
 
-        subparsers = parser.add_subparsers(metavar="COMMAND", help="Command Help", required=True)
+        subparsers = add_subparsers(parser, metavar="COMMAND", help="Command Help", required=True)
         for _, command_info in SubCommandMixin._find_command_infos(target):
             command_actions = []
             command_func = getattr(target, command_info.func.__name__)
diff --git a/src/linktools/cli/commands/common/tools.py b/src/linktools/cli/commands/common/tools.py
index 3d428bda..248416eb 100755
--- a/src/linktools/cli/commands/common/tools.py
+++ b/src/linktools/cli/commands/common/tools.py
@@ -33,7 +33,7 @@
 
 from linktools import ToolError
 from linktools.cli import BaseCommand
-from linktools.cli.argparse import KeyValueAction
+from linktools.cli.argparse import KeyValueAction, add_subparsers
 from linktools.utils import DownloadError
 
 
@@ -61,7 +61,7 @@ def init_arguments(self, parser: ArgumentParser) -> None:
                            help="execute tools as a daemon")
 
         tool_names = sorted([tool.name for tool in iter(self.environ.tools)])
-        subparsers = parser.add_subparsers(metavar="TOOL", help=f"{{{','.join(tool_names)}}}", required=True)
+        subparsers = add_subparsers(parser, metavar="TOOL", help=f"{{{','.join(tool_names)}}}", required=True)
         for tool_name in tool_names:
             tool_parser = subparsers.add_parser(tool_name, prefix_chars=chr(0))
             tool_parser.add_argument("tool_args", metavar="args", nargs="...")
diff --git a/src/linktools/utils/_utils.py b/src/linktools/utils/_utils.py
index d9e7e2af..127c7e61 100755
--- a/src/linktools/utils/_utils.py
+++ b/src/linktools/utils/_utils.py
@@ -34,6 +34,7 @@
 import random
 import re
 import socket
+import sys
 import threading
 import time
 import typing
@@ -406,20 +407,21 @@ def get_path(root_path: str, *paths: [str], create: bool = False, create_parent:
     return target_path
 
 
-@typing.overload
-def read_file(path: str) -> bytes: ...
+if sys.version_info >= (3, 8):
+    @typing.overload
+    def read_file(path: str) -> bytes: ...
 
 
-@typing.overload
-def read_file(path: str, binary: typing.Literal[True]) -> bytes: ...
+    @typing.overload
+    def read_file(path: str, binary: typing.Literal[True]) -> bytes: ...
 
 
-@typing.overload
-def read_file(path: str, binary: typing.Literal[False]) -> str: ...
+    @typing.overload
+    def read_file(path: str, binary: typing.Literal[False]) -> str: ...
 
 
-@typing.overload
-def read_file(path: str, binary: bool) -> Union[str, bytes]: ...
+    @typing.overload
+    def read_file(path: str, binary: bool) -> Union[str, bytes]: ...
 
 
 def read_file(path: str, binary: bool = True) -> Union[str, bytes]: