feat: use local version of BooleanOptionalAction to support Python …

…3.7 and 3.8

corgy/_corgy.py

@@ -32,6 +32,29 @@
 _T = TypeVar("_T", bound="Corgy")
 
 
+class BooleanOptionalAction(argparse.Action):
+    # :meta private:
+    # Backport of `argparse.BooleanOptionalAction` from Python 3.9.
+    # Taken almost verbatim from `CPython/Lib/argparse.py`.
+    def __init__(self, option_strings, dest, *args, **kwargs):
+
+        _option_strings = []
+        for option_string in option_strings:
+            _option_strings.append(option_string)
+
+            if option_string.startswith("--"):
+                option_string = "--no-" + option_string[2:]
+                _option_strings.append(option_string)
+
+        super().__init__(
+            option_strings=_option_strings, dest=dest, nargs=0, *args, **kwargs
+        )
+
+    def __call__(self, parser, namespace, values, option_string=None):
+        if option_string in self.option_strings:
+            setattr(namespace, self.dest, not option_string.startswith("--no-"))
+
+
 class _CorgyMeta(type):
     """Metaclass for `Corgy`.
 
@@ -312,8 +335,7 @@ class A:
         x: A
 
     **Bool**
-    `bool` types (when not in a sequence) are converted to
-    `argparse.BooleanOptionalAction` on Python 3.9 and above::
+    `bool` types (when not in a sequence) are converted to a pair of options::
 
         class A(Corgy):
             arg: bool
@@ -487,7 +509,7 @@ def add_args_to_parser(
             # `--<var-name>`/`--no-<var-name>` arguments.
             var_action: Optional[Type[argparse.Action]]
             if var_base_type is bool and var_nargs is None:
-                var_action = getattr(argparse, "BooleanOptionalAction", None)
+                var_action = BooleanOptionalAction
             else:
                 var_action = None
 

corgy/_helpfmt.py

@@ -11,9 +11,6 @@
 from typing import Optional, Sequence, Tuple, Union
 from unittest.mock import patch
 
-if sys.version_info >= (3, 9):
-    from argparse import BooleanOptionalAction
-
 __all__ = ("CorgyHelpFormatter",)
 
 # These placeholders are used to replace special characters and words, so they can be
@@ -213,10 +210,6 @@ def using_colors(self) -> bool:
         re.DOTALL,
     )
 
-    # Regex to match the default value added to help by `BooleanOptionalAction`.
-    if sys.version_info >= (3, 9):
-        _pattern_bool_opt_default = re.compile(r" \(default: .*\)")
-
     @staticmethod
     @lru_cache(maxsize=None)
     def _pattern_placeholder_text(placeholder: str) -> re.Pattern:
@@ -420,12 +413,6 @@ def _format_action(self, action: Action) -> str:
                     f"default: {self._stringify(action.default, action.type)}"
                 )
 
-            if sys.version_info >= (3, 9):
-                if isinstance(action, BooleanOptionalAction) and action.help:
-                    # BooleanOptionalAction adds the default value to the help text.
-                    # Remove it, since we already have it.
-                    action.help = self._pattern_bool_opt_default.sub("", action.help)
-
         # Add qualifier to choice list e.g. `({a/b/c} required)`.
         if choice_list_fmt or arg_qualifier:
             if self.using_colors:

docs/corgy.md

@@ -205,8 +205,7 @@ x: A
 ```
 
 **Bool**
-`bool` types (when not in a sequence) are converted to
-`argparse.BooleanOptionalAction` on Python 3.9 and above:
+`bool` types (when not in a sequence) are converted to a pair of options:
 
 ```python
 class A(Corgy):

tests/test_corgy.py

@@ -20,6 +20,7 @@
 
 import corgy
 from corgy import Corgy, CorgyHelpFormatter, corgyparser
+from corgy._corgy import BooleanOptionalAction
 
 
 class TestCorgyMeta(unittest.TestCase):
@@ -370,24 +371,22 @@ class C(Corgy):
         C.add_args_to_parser(self.parser)
         self.parser.add_argument.assert_called_once_with("--x", type=T, default=t)
 
-    @skipIf(sys.version_info < (3, 9), "`BooleanOptionalAction` unavailable")
     def test_add_args_converts_bool_to_action(self):
         class C(Corgy):
             x: bool
 
         C.add_args_to_parser(self.parser)
         self.parser.add_argument.assert_called_once_with(
-            "--x", type=bool, action=argparse.BooleanOptionalAction, required=True
+            "--x", type=bool, action=BooleanOptionalAction, required=True
         )
 
-    @skipIf(sys.version_info < (3, 9), "`BooleanOptionalAction` unavailable")
     def test_add_args_handles_default_for_bool_type(self):
         class C(Corgy):
             x: bool = False
 
         C.add_args_to_parser(self.parser)
         self.parser.add_argument.assert_called_once_with(
-            "--x", type=bool, action=argparse.BooleanOptionalAction, default=False
+            "--x", type=bool, action=BooleanOptionalAction, default=False
         )
 
     def test_add_args_does_not_convert_bool_sequence_to_action(self):

tests/test_helpfmt.py

@@ -1,14 +1,11 @@
-import sys
 from argparse import ArgumentParser, SUPPRESS
 from unittest import skipIf, TestCase
 from unittest.mock import Mock, patch
 
 from corgy import CorgyHelpFormatter
+from corgy._corgy import BooleanOptionalAction
 from corgy._helpfmt import _ColorHelper
 
-if sys.version_info >= (3, 9):
-    from argparse import BooleanOptionalAction
-
 _COLOR_HELPER = _ColorHelper(skip_tty_check=True)
 _CRAYONS = _COLOR_HELPER.crayons
 
@@ -366,7 +363,6 @@ def test_corgy_help_formatter_handles_different_prefix_chars(self):
                 f"  {_O('+++x')} {_M('str')}  x help ({_K('optional')})",
             )
 
-    @skipIf(sys.version_info < (3, 9), "`BooleanOptionalAction` not available")
     def test_corgy_help_formatter_handles_boolean_optional_action(self):
         self.assertEqual(
             self._get_arg_help(