Fix bug where --si=64 was deemed ambiguous when both --si and --size were in the parser.

2 files changed, 26 insertions, 0 deletions

diff --git a/argparse.py b/argparse.py
index 16a778f..8b96e62 100644
--- a/argparse.py
+++ b/argparse.py
@@ -2036,6 +2036,13 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
             action = self._option_string_actions[arg_string]
             return action, arg_string, None
 
+        # if the option string before the "=" is present, return the action
+        if '=' in arg_string:
+            option_string, explicit_arg = arg_string.split('=', 1)
+            if option_string in self._option_string_actions:
+                action = self._option_string_actions[option_string]
+                return action, option_string, explicit_arg
+
         # search through all possible prefixes of the option string
         # and all actions in the parser for possible interpretations
         option_tuples = self._get_option_tuples(arg_string)
diff --git a/test/test_argparse.py b/test/test_argparse.py
index 2356389..a7eb74a 100644
--- a/test/test_argparse.py
+++ b/test/test_argparse.py
@@ -401,6 +401,25 @@ class TestOptionalsDoubleDashPartialMatch(ParserTestCase):
     ]
 
 
+class TestOptionalsDoubleDashPrefixMatch(ParserTestCase):
+    """Tests when one double-dash option string is a prefix of another"""
+
+    argument_signatures = [
+        Sig('--badger', action='store_true'),
+        Sig('--ba'),
+    ]
+    failures = ['--bar', '--b', '--ba', '--b=2', '--badge 5']
+    successes = [
+        ('', NS(badger=False, ba=None)),
+        ('--ba X', NS(badger=False, ba='X')),
+        ('--ba=X', NS(badger=False, ba='X')),
+        ('--bad', NS(badger=True, ba=None)),
+        ('--badg', NS(badger=True, ba=None)),
+        ('--badge', NS(badger=True, ba=None)),
+        ('--badger', NS(badger=True, ba=None)),
+    ]
+
+
 class TestOptionalsSingleDoubleDash(ParserTestCase):
     """Test an Optional with single- and double-dash option strings"""