Fix #171: add an ignored `default=` argument to our custom actions.

This is a required argument for custom argparse.Action classes, and is used when the `ArgumentParse` is created with a `argument_default=`.

PiperOrigin-RevId: 385601086
Change-Id: I01ef4870aa4f0e92f7e8f9be0125c9a0dba16c6f

3 files changed, 37 insertions, 5 deletions

diff --git a/absl/CHANGELOG.md b/absl/CHANGELOG.md
index aff590d..253628f 100644
--- a/absl/CHANGELOG.md
+++ b/absl/CHANGELOG.md
@@ -6,7 +6,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com).
 
 ## Unreleased
 
-Nothing notable unreleased.
+### Fixed
+
+*   #171: Creating `argparse_flags.ArgumentParser` with `argument_default=` no
+    longer raises an exception when other `absl.flags` flags are defined.
 
 ## 0.13.0 (2021-06-14)
 
diff --git a/absl/flags/argparse_flags.py b/absl/flags/argparse_flags.py
index ea4cdfa..4f78f50 100644
--- a/absl/flags/argparse_flags.py
+++ b/absl/flags/argparse_flags.py
@@ -148,7 +148,8 @@ class ArgumentParser(argparse.ArgumentParser):
           default=argparse.SUPPRESS, help='show full help message and exit')
 
     if self._inherited_absl_flags:
-      self.add_argument('--undefok', help=argparse.SUPPRESS)
+      self.add_argument(
+          '--undefok', default=argparse.SUPPRESS, help=argparse.SUPPRESS)
       self._define_absl_flags(self._inherited_absl_flags)
 
   def parse_known_args(self, args=None, namespace=None):
@@ -237,7 +238,14 @@ class ArgumentParser(argparse.ArgumentParser):
 class _FlagAction(argparse.Action):
   """Action class for Abseil non-boolean flags."""
 
-  def __init__(self, option_strings, dest, help, metavar, flag_instance):  # pylint: disable=redefined-builtin
+  def __init__(
+      self,
+      option_strings,
+      dest,
+      help,  # pylint: disable=redefined-builtin
+      metavar,
+      flag_instance,
+      default=argparse.SUPPRESS):
     """Initializes _FlagAction.
 
     Args:
@@ -246,6 +254,8 @@ class _FlagAction(argparse.Action):
       help: See argparse.Action.
       metavar: See argparse.Action.
       flag_instance: absl.flags.Flag, the absl flag instance.
+      default: Ignored. The flag always uses dest=argparse.SUPPRESS so it
+          doesn't affect the parsing result.
     """
     del dest
     self._flag_instance = flag_instance
@@ -264,7 +274,14 @@ class _FlagAction(argparse.Action):
 class _BooleanFlagAction(argparse.Action):
   """Action class for Abseil boolean flags."""
 
-  def __init__(self, option_strings, dest, help, metavar, flag_instance):  # pylint: disable=redefined-builtin
+  def __init__(
+      self,
+      option_strings,
+      dest,
+      help,  # pylint: disable=redefined-builtin
+      metavar,
+      flag_instance,
+      default=argparse.SUPPRESS):
     """Initializes _BooleanFlagAction.
 
     Args:
@@ -273,8 +290,10 @@ class _BooleanFlagAction(argparse.Action):
       help: See argparse.Action.
       metavar: See argparse.Action.
       flag_instance: absl.flags.Flag, the absl flag instance.
+      default: Ignored. The flag always uses dest=argparse.SUPPRESS so it
+          doesn't affect the parsing result.
     """
-    del dest
+    del dest, default
     self._flag_instance = flag_instance
     flag_names = [self._flag_instance.name]
     if self._flag_instance.short_name:
diff --git a/absl/flags/tests/argparse_flags_test.py b/absl/flags/tests/argparse_flags_test.py
index ddd62a9..a2bcbe5 100644
--- a/absl/flags/tests/argparse_flags_test.py
+++ b/absl/flags/tests/argparse_flags_test.py
@@ -36,6 +36,7 @@ import six
 class ArgparseFlagsTest(parameterized.TestCase):
 
   def setUp(self):
+    super().setUp()
     self._absl_flags = flags.FlagValues()
     flags.DEFINE_bool(
         'absl_bool', None, 'help for --absl_bool.',
@@ -393,6 +394,15 @@ class ArgparseFlagsTest(parameterized.TestCase):
     with self.assertRaises(SystemExit):
       parser.parse_args(cmd_args)
 
+  def test_argument_default(self):
+    # Regression test for https://github.com/abseil/abseil-py/issues/171.
+    parser = argparse_flags.ArgumentParser(
+        inherited_absl_flags=self._absl_flags, argument_default=23)
+    parser.add_argument(
+        '--magic_number', type=int, help='The magic number to use.')
+    args = parser.parse_args([])
+    self.assertEqual(args.magic_number, 23)
+
 
 class ArgparseWithAppRunTest(parameterized.TestCase):