Add convert_choices to add_argument

This allows users to specify choices in the same vocabulary as the user will enter them.

Author: hansthen

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, convert_choices=False)
+                          suggest_on_error=False)
 
    Create a new :class:`ArgumentParser` object. All parameters should be passed
    as keyword arguments. Each parameter has its own more detailed description
@@ -119,9 +119,6 @@ ArgumentParser objects
    * suggest_on_error_ - Enables suggestions for mistyped argument choices
      and subparser names (default: ``False``)
 
-   * convert_choices_ - Runs the ``choices`` through the ``type`` callable
-     during checking (default: ``False``)
-
 
    .. versionchanged:: 3.5
       *allow_abbrev* parameter was added.
@@ -615,38 +612,6 @@ keyword argument::
 .. versionadded:: 3.14
 
 
-convert_choices
-^^^^^^^^^^^^^^^
-
-By default, when a user passes both a ``type`` and a ``choices`` argument, the
-``choices`` need to be specified in the target type, after conversion.
-This can cause confusing ``usage`` and ``help`` strings. If the user would like
-to specify ``choices`` in the same vocabulary as the end-user would enter them,
-this feature can be enabled by setting ``convert_choices`` to ``True``::
-
-   >>> parser = argparse.ArgumentParser(convert_choices=True)
-   >>> parser.add_argument('when',
-   ...                     choices=['mo', 'tu', 'we', 'th', 'fr', 'sa', 'su'],
-   ...                     type=to_dow)
-   >>> parser.print_help()
-   usage: example_broken.py [-h] [--days {mo,tu,we,th,fr,sa,su}]
-
-   options:
-     -h, --help            show this help message and exit
-     --days {mo,tu,we,th,fr,sa,su}
-
-
-If you're writing code that needs to be compatible with older Python versions
-and want to opportunistically use ``convert_choices`` when it's available, you
-can set it as an attribute after initializing the parser instead of using the
-keyword argument::
-
-   >>> parser = argparse.ArgumentParser()
-   >>> parser.convert_choices = True
-
-.. versionadded:: next
-
-
 The add_argument() method
 -------------------------
 
@@ -674,6 +639,9 @@ The add_argument() method
 
    * choices_ - A sequence of the allowable values for the argument.
 
+   * convert_choices_ - Whether to convert the choices_ using the type_ callable
+     before checking.
+
    * required_ - Whether or not the command-line option may be omitted
      (optionals only).
 
@@ -1159,24 +1127,39 @@ if the argument was not one of the acceptable values::
    game.py: error: argument move: invalid choice: 'fire' (choose from 'rock',
    'paper', 'scissors')
 
-Note that, by default, inclusion in the *choices* sequence is checked after
-any type_ conversions have been performed, so the type of the objects in the
-*choices* sequence should match the type_ specified. This can lead to
-confusing ``usage`` messages. If you want to convert *choices* using type_
-before checking, set the ``convert_choices`` flag on :class:`~ArgumentParser`.
-
-
 Any sequence can be passed as the *choices* value, so :class:`list` objects,
 :class:`tuple` objects, and custom sequences are all supported.
 
-Use of :class:`enum.Enum` is not recommended because it is difficult to
-control its appearance in usage, help, and error messages.
-
 Formatted choices override the default *metavar* which is normally derived
 from *dest*.  This is usually what you want because the user never sees the
 *dest* parameter.  If this display isn't desirable (perhaps because there are
 many choices), just specify an explicit metavar_.
 
+.. _convert_choices:
+
+convert_choices
+^^^^^^^^^^^^^^^
+
+By default, when a user passes both a ``type`` and a ``choices`` argument, the
+``choices`` need to be specified in the target type, after conversion.
+This can cause confusing ``usage`` and ``help`` strings. If the user would like
+to specify ``choices`` in the same vocabulary as the end-user would enter them,
+this feature can be enabled by setting ``convert_choices`` to ``True``::
+
+   >>> parser = argparse.ArgumentParser()
+   >>> parser.add_argument('when',
+   ...                     choices=['mo', 'tu', 'we', 'th', 'fr', 'sa', 'su'],
+   ...                     convert_choices=True,
+   ...                     type=to_dow)
+   >>> parser.print_help()
+   usage: example_broken.py [-h] [--days {mo,tu,we,th,fr,sa,su}]
+
+   options:
+     -h, --help            show this help message and exit
+     --days {mo,tu,we,th,fr,sa,su}
+
+.. versionadded:: next
+
 
 .. _required:
 

Lib/argparse.py

@@ -792,6 +792,9 @@ class Action(_AttributeHolder):
             type, an exception will be raised if it is not a member of this
             collection.
 
+        - convert_choices - Runs the ``choices`` through the ``type`` callable
+            during checking. (default: ``False``)
+
         - required -- True if the action must always be specified at the
             command line. This is only meaningful for optional command-line
             arguments.
@@ -810,6 +813,7 @@ def __init__(self,
                  default=None,
                  type=None,
                  choices=None,
+                 convert_choices=False,
                  required=False,
                  help=None,
                  metavar=None,
@@ -821,6 +825,7 @@ def __init__(self,
         self.default = default
         self.type = type
         self.choices = choices
+        self.convert_choices = convert_choices
         self.required = required
         self.help = help
         self.metavar = metavar
@@ -835,6 +840,7 @@ def _get_kwargs(self):
             'default',
             'type',
             'choices',
+            'convert_choices',
             'required',
             'help',
             'metavar',
@@ -897,6 +903,7 @@ def __init__(self,
                  default=None,
                  type=None,
                  choices=None,
+                 convert_choices=False,
                  required=False,
                  help=None,
                  metavar=None,
@@ -915,6 +922,7 @@ def __init__(self,
             default=default,
             type=type,
             choices=choices,
+            convert_choices=convert_choices,
             required=required,
             help=help,
             metavar=metavar,
@@ -1777,8 +1785,6 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
             error info when an error occurs
         - suggest_on_error - Enables suggestions for mistyped argument choices
             and subparser names. (default: ``False``)
-        - convert_choices - Runs the ``choices`` through the ``type`` callable
-            during checking. (default: ``False``)
     """
 
     def __init__(self,
@@ -1795,8 +1801,7 @@ def __init__(self,
                  add_help=True,
                  allow_abbrev=True,
                  exit_on_error=True,
-                 suggest_on_error=False,
-                 convert_choices=False):
+                 suggest_on_error=False):
 
         superinit = super(ArgumentParser, self).__init__
         superinit(description=description,
@@ -1813,7 +1818,6 @@ def __init__(self,
         self.allow_abbrev = allow_abbrev
         self.exit_on_error = exit_on_error
         self.suggest_on_error = suggest_on_error
-        self.convert_choices = convert_choices
 
         add_group = self.add_argument_group
         self._positionals = add_group(_('positional arguments'))
@@ -2589,9 +2593,8 @@ def _check_value(self, action, value, arg_string=None):
             choices = iter(choices)
 
         typed_choices = []
-        if (self.convert_choices and
-            action.type and
-            all(isinstance(choice, str) for choice in choices)
+        if (action.convert_choices and
+            action.type
         ):
             typed_choices = [action.type(v) for v in choices]
 

Lib/test/test_argparse.py

@@ -1957,10 +1957,11 @@ def to_dow(arg):
 class TestTypedChoices(TestChoices):
     """Test a set of string choices that convert to weekdays"""
 
-    parser_signature = Sig(convert_choices=True)
     argument_signatures = [
         Sig('when',
-            type=TestChoices.to_dow, choices=["mo", "tu", "we" , "th", "fr", "sa", "su"],
+            type=TestChoices.to_dow,
+            choices=["mo", "tu", "we" , "th", "fr", "sa", "su"],
+            convert_choices=True,
         )
     ]
 
@@ -5518,11 +5519,12 @@ def to_date(arg):
         else:
             return None
 
-    parser_signature = Sig(prog='PROG', convert_choices=True)
+    parser_signature = Sig(prog='PROG')
     argument_signatures = [
         Sig('when',
             type=to_date,
-            choices=["today", "tomorrow"]
+            choices=["today", "tomorrow"],
+            convert_choices=True
         ),
     ]
 
@@ -5932,7 +5934,8 @@ def test_optional(self):
         string = (
             "Action(option_strings=['--foo', '-a', '-b'], dest='b', "
             "nargs='+', const=None, default=42, type='int', "
-            "choices=[1, 2, 3], required=False, help='HELP', "
+            "choices=[1, 2, 3], convert_choices=False, "
+            "required=False, help='HELP', "
             "metavar='METAVAR', deprecated=False)")
         self.assertStringEqual(option, string)
 
@@ -5950,6 +5953,7 @@ def test_argument(self):
         string = (
             "Action(option_strings=[], dest='x', nargs='?', "
             "const=None, default=2.5, type=%r, choices=[0.5, 1.5, 2.5], "
+            "convert_choices=False, "
             "required=True, help='H HH H', metavar='MV MV MV', "
             "deprecated=False)" % float)
         self.assertStringEqual(argument, string)