From d5e7348e4105d1d4a1c5bd1087f61041532ecbf3 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Fri, 5 Jun 2020 19:31:18 -0700
Subject: bpo-40862: Raise TypeError when const is given to
 argparse.BooleanOptionalAction (GH-20623) (GH-20664)

---
 Lib/argparse.py           | 1 -
 Lib/test/test_argparse.py | 8 ++++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/Lib/argparse.py b/Lib/argparse.py
index 2677ef6..2fb1da5 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -857,7 +857,6 @@ class BooleanOptionalAction(Action):
     def __init__(self,
                  option_strings,
                  dest,
-                 const=None,
                  default=None,
                  type=None,
                  choices=None,
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index e82a0c3..22cae62 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -700,6 +700,14 @@ class TestBooleanOptionalAction(ParserTestCase):
         ('--no-foo --foo', NS(foo=True)),
     ]
 
+    def test_const(self):
+        # See bpo-40862
+        parser = argparse.ArgumentParser()
+        with self.assertRaises(TypeError) as cm:
+            parser.add_argument('--foo', const=True, action=argparse.BooleanOptionalAction)
+
+        self.assertIn("got an unexpected keyword argument 'const'", str(cm.exception))
+
 class TestBooleanOptionalActionRequired(ParserTestCase):
     """Tests BooleanOptionalAction required"""
 
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