pythongh-140448: Default suggest_on_error to True in argparse.ArgumentParser (python#140450)

Author: HomerusJa

Doc/library/argparse.rst

@@ -74,7 +74,7 @@ ArgumentParser objects
                           prefix_chars='-', fromfile_prefix_chars=None, \
                           argument_default=None, conflict_handler='error', \
                           add_help=True, allow_abbrev=True, exit_on_error=True, \
-                          *, suggest_on_error=False, color=True)
+                          *, suggest_on_error=True, color=True)
 
    Create a new :class:`ArgumentParser` object. All parameters should be passed
    as keyword arguments. Each parameter has its own more detailed description
@@ -117,7 +117,7 @@ ArgumentParser objects
      error info when an error occurs. (default: ``True``)
 
    * suggest_on_error_ - Enables suggestions for mistyped argument choices
-     and subparser names (default: ``False``)
+     and subparser names (default: ``True``)
 
    * color_ - Allow color output (default: ``True``)
 
@@ -134,6 +134,9 @@ ArgumentParser objects
    .. versionchanged:: 3.14
       *suggest_on_error* and *color* parameters were added.
 
+   .. versionchanged:: 3.15
+      *suggest_on_error* default changed to ``True``.
+
 The following sections describe how each of these are used.
 
 
@@ -596,13 +599,11 @@ suggest_on_error
 ^^^^^^^^^^^^^^^^
 
 By default, when a user passes an invalid argument choice or subparser name,
-:class:`ArgumentParser` will exit with error info and list the permissible
-argument choices (if specified) or subparser names as part of the error message.
-
-If the user would like to enable suggestions for mistyped argument choices and
-subparser names, the feature can be enabled by setting ``suggest_on_error`` to
-``True``. Note that this only applies for arguments when the choices specified
-are strings::
+:class:`ArgumentParser` will exit with error info and provide suggestions for
+mistyped arguments. The error message will list the permissible argument
+choices (if specified) or subparser names, along with a "maybe you meant"
+suggestion if a close match is found. Note that this only applies for arguments
+when the choices specified are strings::
 
    >>> parser = argparse.ArgumentParser(description='Process some integers.',
                                         suggest_on_error=True)
@@ -612,16 +613,14 @@ are strings::
    >>> parser.parse_args(['--action', 'sumn', 1, 2, 3])
    tester.py: error: argument --action: invalid choice: 'sumn', maybe you meant 'sum'? (choose from 'sum', 'max')
 
-If you're writing code that needs to be compatible with older Python versions
-and want to opportunistically use ``suggest_on_error`` when it's available, you
-can set it as an attribute after initializing the parser instead of using the
-keyword argument::
+You can disable suggestions by setting ``suggest_on_error`` to ``False``::
 
-   >>> parser = argparse.ArgumentParser(description='Process some integers.')
-   >>> parser.suggest_on_error = True
+   >>> parser = argparse.ArgumentParser(description='Process some integers.',
+                                        suggest_on_error=False)
 
 .. versionadded:: 3.14
-
+.. versionchanged:: 3.15
+   Changed default value of ``suggest_on_error`` from ``False`` to ``True``.
 
 color
 ^^^^^

Doc/whatsnew/3.15.rst

@@ -317,6 +317,13 @@ New modules
 Improved modules
 ================
 
+argparse
+--------
+
+* Changed the *suggest_on_error* parameter of :class:`argparse.ArgumentParser` to
+  default to ``True``. This enables suggestions for mistyped arguments by default.
+  (Contributed by Jakob Schluse in :gh:`140450`.)
+
 calendar
 --------
 

Lib/argparse.py

@@ -1857,7 +1857,7 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
         - exit_on_error -- Determines whether or not ArgumentParser exits with
             error info when an error occurs
         - suggest_on_error - Enables suggestions for mistyped argument choices
-            and subparser names (default: ``False``)
+            and subparser names (default: ``True``)
         - color - Allow color output in help messages (default: ``False``)
     """
 
@@ -1876,7 +1876,7 @@ def __init__(self,
                  allow_abbrev=True,
                  exit_on_error=True,
                  *,
-                 suggest_on_error=False,
+                 suggest_on_error=True,
                  color=True,
                  ):
         superinit = super(ArgumentParser, self).__init__

Lib/test/test_argparse.py

@@ -2287,7 +2287,7 @@ class TestArgumentAndSubparserSuggestions(TestCase):
     """Test error handling and suggestion when a user makes a typo"""
 
     def test_wrong_argument_error_with_suggestions(self):
-        parser = ErrorRaisingArgumentParser(suggest_on_error=True)
+        parser = ErrorRaisingArgumentParser()
         parser.add_argument('foo', choices=['bar', 'baz'])
         with self.assertRaises(ArgumentParserError) as excinfo:
             parser.parse_args(('bazz',))
@@ -2307,7 +2307,7 @@ def test_wrong_argument_error_no_suggestions(self):
         )
 
     def test_wrong_argument_subparsers_with_suggestions(self):
-        parser = ErrorRaisingArgumentParser(suggest_on_error=True)
+        parser = ErrorRaisingArgumentParser()
         subparsers = parser.add_subparsers(required=True)
         subparsers.add_parser('foo')
         subparsers.add_parser('bar')
@@ -2331,18 +2331,19 @@ def test_wrong_argument_subparsers_no_suggestions(self):
             excinfo.exception.stderr,
         )
 
-    def test_wrong_argument_no_suggestion_implicit(self):
-        parser = ErrorRaisingArgumentParser()
+    def test_wrong_argument_with_suggestion_explicit(self):
+        parser = ErrorRaisingArgumentParser(suggest_on_error=True)
         parser.add_argument('foo', choices=['bar', 'baz'])
         with self.assertRaises(ArgumentParserError) as excinfo:
             parser.parse_args(('bazz',))
         self.assertIn(
-            "error: argument foo: invalid choice: 'bazz' (choose from bar, baz)",
+            "error: argument foo: invalid choice: 'bazz', maybe you meant"
+             " 'baz'? (choose from bar, baz)",
             excinfo.exception.stderr,
         )
 
     def test_suggestions_choices_empty(self):
-        parser = ErrorRaisingArgumentParser(suggest_on_error=True)
+        parser = ErrorRaisingArgumentParser()
         parser.add_argument('foo', choices=[])
         with self.assertRaises(ArgumentParserError) as excinfo:
             parser.parse_args(('bazz',))
@@ -2352,7 +2353,7 @@ def test_suggestions_choices_empty(self):
         )
 
     def test_suggestions_choices_int(self):
-        parser = ErrorRaisingArgumentParser(suggest_on_error=True)
+        parser = ErrorRaisingArgumentParser()
         parser.add_argument('foo', choices=[1, 2])
         with self.assertRaises(ArgumentParserError) as excinfo:
             parser.parse_args(('3',))
@@ -2362,7 +2363,7 @@ def test_suggestions_choices_int(self):
         )
 
     def test_suggestions_choices_mixed_types(self):
-        parser = ErrorRaisingArgumentParser(suggest_on_error=True)
+        parser = ErrorRaisingArgumentParser()
         parser.add_argument('foo', choices=[1, '2'])
         with self.assertRaises(ArgumentParserError) as excinfo:
             parser.parse_args(('3',))

Misc/ACKS

@@ -1681,6 +1681,7 @@ David Scherer
 Wolfgang Scherer
 Felix Scherz
 Hynek Schlawack
+Jakob Schluse
 Bob Schmertz
 Gregor Schmid
 Ralf Schmitt

Misc/NEWS.d/next/Library/2025-10-22-12-56-57.gh-issue-140448.GsEkXD.rst

@@ -0,0 +1,2 @@
+Change the default of ``suggest_on_error`` to ``True`` in
+``argparse.ArgumentParser``.