pythongh-124305: argparse no longer eats initial '=' from short optio…

…n argument

Lib/argparse.py

@@ -2009,11 +2009,9 @@ def consume_optional(start_index):
                             explicit_arg = explicit_arg[1:]
                             if not explicit_arg:
                                 sep = explicit_arg = None
-                            elif explicit_arg[0] == '=':
-                                sep = '='
-                                explicit_arg = explicit_arg[1:]
                             else:
                                 sep = ''
+                            continue
                         else:
                             extras.append(char + explicit_arg)
                             stop = start_index + 1
@@ -2261,7 +2259,11 @@ def _parse_optional(self, arg_string):
         option_string, sep, explicit_arg = arg_string.partition('=')
         if sep and option_string in self._option_string_actions:
             action = self._option_string_actions[option_string]
-            return action, option_string, sep, explicit_arg
+            if arg_string[1] not in self.prefix_chars and len(option_string) == 2:
+                # Short option with an argument starting with "=".
+                return action, option_string, None, sep + explicit_arg
+            else:
+                return action, option_string, sep, explicit_arg
 
         # search through all possible prefixes of the option string
         # and all actions in the parser for possible interpretations

Lib/test/test_argparse.py

@@ -313,6 +313,7 @@ class TestOptionalsSingleDash(ParserTestCase):
         ('', NS(x=None)),
         ('-x a', NS(x='a')),
         ('-xa', NS(x='a')),
+        ('-x=a', NS(x='=a')),
         ('-x -1', NS(x='-1')),
         ('-x-1', NS(x='-1')),
     ]
@@ -334,6 +335,7 @@ class TestOptionalsSingleDashCombined(ParserTestCase):
         ('-za', NS(x=False, yyy=None, z='a')),
         ('-z a', NS(x=False, yyy=None, z='a')),
         ('-xza', NS(x=True, yyy=None, z='a')),
+        ('-xz=a', NS(x=True, yyy=None, z='=a')),
         ('-xz a', NS(x=True, yyy=None, z='a')),
         ('-x -za', NS(x=True, yyy=None, z='a')),
         ('-x -z a', NS(x=True, yyy=None, z='a')),
@@ -348,10 +350,12 @@ class TestOptionalsSingleDashLong(ParserTestCase):
     """Test an Optional with a multi-character single-dash option string"""
 
     argument_signatures = [Sig('-foo')]
-    failures = ['-foo', 'a', '--foo', '-foo --foo', '-foo -y', '-fooa']
+    failures = ['-foo', 'a', '--foo', '-foo --foo', '-foo -y', '-fooa',
+                '-foa', '-fa', '-fo=a', '-f=a']
     successes = [
         ('', NS(foo=None)),
         ('-foo a', NS(foo='a')),
+        ('-foo=a', NS(foo='a')),
         ('-foo -1', NS(foo='-1')),
         ('-fo a', NS(foo='a')),
         ('-f a', NS(foo='a')),
@@ -2263,19 +2267,22 @@ def test_parse_known_args_with_single_dash_option(self):
                          (NS(known=1, new=0), ['-u']))
         self.assertEqual(parser.parse_known_args(['-ku']),
                          (NS(known=1, new=0), ['-u']))
-        self.assertArgumentParserError(parser.parse_known_args, ['-k=u'])
+        self.assertEqual(parser.parse_known_args(['-k=u']),
+                         (NS(known=1, new=0), ['-=u']))
         self.assertEqual(parser.parse_known_args(['-uk']),
                          (NS(known=0, new=0), ['-uk']))
         self.assertEqual(parser.parse_known_args(['-u=k']),
                          (NS(known=0, new=0), ['-u=k']))
         self.assertEqual(parser.parse_known_args(['-kunknown']),
                          (NS(known=1, new=0), ['-unknown']))
-        self.assertArgumentParserError(parser.parse_known_args, ['-k=unknown'])
+        self.assertEqual(parser.parse_known_args(['-k=unknown']),
+                         (NS(known=1, new=0), ['-=unknown']))
         self.assertEqual(parser.parse_known_args(['-ku=nknown']),
                          (NS(known=1, new=0), ['-u=nknown']))
         self.assertEqual(parser.parse_known_args(['-knew']),
                          (NS(known=1, new=1), ['-ew']))
-        self.assertArgumentParserError(parser.parse_known_args, ['-kn=ew'])
+        self.assertEqual(parser.parse_known_args(['-kn=ew']),
+                         (NS(known=1, new=1), ['-=ew']))
         self.assertArgumentParserError(parser.parse_known_args, ['-k-new'])
         self.assertArgumentParserError(parser.parse_known_args, ['-kn-ew'])
         self.assertEqual(parser.parse_known_args(['-kne-w']),

Misc/NEWS.d/next/Library/2024-09-23-15-38-03.gh-issue-124305.7mQPyn.rst

@@ -0,0 +1 @@
+:mod:`argparse` no longer eats initial '=' from short option argument.