Issue #11174: Add argparse.MetavarTypeHelpFormatter, which uses type names

for the names of optional and positional arguments in help messages.

Doc/library/argparse.rst

@@ -356,13 +356,10 @@ formatter_class
 ^^^^^^^^^^^^^^^
 
 :class:`ArgumentParser` objects allow the help formatting to be customized by
-specifying an alternate formatting class.  Currently, there are three such
+specifying an alternate formatting class.
-classes: :class:`argparse.RawDescriptionHelpFormatter`,
-:class:`argparse.RawTextHelpFormatter` and
-:class:`argparse.ArgumentDefaultsHelpFormatter`.  The first two allow more
-control over how textual descriptions are displayed, while the last
-automatically adds information about argument default values.
 
+:class:`RawDescriptionHelpFormatter` and :class:`RawTextHelpFormatter` give
+more control over how textual descriptions are displayed.
 By default, :class:`ArgumentParser` objects line-wrap the description_ and
 epilog_ texts in command-line help messages::
 
@@ -386,7 +383,7 @@ epilog_ texts in command-line help messages::
    likewise for this epilog whose whitespace will be cleaned up and whose words
    will be wrapped across a couple lines
 
-Passing :class:`argparse.RawDescriptionHelpFormatter` as ``formatter_class=``
+Passing :class:`RawDescriptionHelpFormatter` as ``formatter_class=``
 indicates that description_ and epilog_ are already correctly formatted and
 should not be line-wrapped::
 
@@ -412,11 +409,11 @@ should not be line-wrapped::
    optional arguments:
     -h, --help  show this help message and exit
 
-:class:`RawTextHelpFormatter` maintains whitespace for all sorts of help text
+:class:`RawTextHelpFormatter` maintains whitespace for all sorts of help text,
 including argument descriptions.
 
-The other formatter class available, :class:`ArgumentDefaultsHelpFormatter`,
+:class:`ArgumentDefaultsHelpFormatter` automatically adds information about
-will add information about the default value of each of the arguments::
+default values to each of the argument help messages::
 
    >>> parser = argparse.ArgumentParser(
    ...     prog='PROG',
@@ -433,6 +430,25 @@ will add information about the default value of each of the arguments::
     -h, --help  show this help message and exit
     --foo FOO   FOO! (default: 42)
 
+:class:`MetavarTypeHelpFormatter` uses the name of the type_ argument for each
+argument as as the display name for its values (rather than using the dest_
+as the regular formatter does)::
+
+   >>> parser = argparse.ArgumentParser(
+   ...     prog='PROG',
+   ...     formatter_class=argparse.MetavarTypeHelpFormatter)
+   >>> parser.add_argument('--foo', type=int)
+   >>> parser.add_argument('bar', type=float)
+   >>> parser.print_help()
+   usage: PROG [-h] [--foo int] float
+
+   positional arguments:
+     float
+
+   optional arguments:
+     -h, --help  show this help message and exit
+     --foo int
+
 
 conflict_handler
 ^^^^^^^^^^^^^^^^

Lib/argparse.py

@@ -71,6 +71,7 @@ __all__ = [
     'ArgumentDefaultsHelpFormatter',
     'RawDescriptionHelpFormatter',
     'RawTextHelpFormatter',
+    'MetavarTypeHelpFormatter',
     'Namespace',
     'Action',
     'ONE_OR_MORE',
@@ -422,7 +423,8 @@ class HelpFormatter(object):
 
             # produce all arg strings
             elif not action.option_strings:
-                part = self._format_args(action, action.dest)
+                default = self._get_default_metavar_for_positional(action)
+                part = self._format_args(action, default)
 
                 # if it's in a group, strip the outer []
                 if action in group_actions:
@@ -444,7 +446,7 @@ class HelpFormatter(object):
                 # if the Optional takes a value, format is:
                 #    -s ARGS or --long ARGS
                 else:
-                    default = action.dest.upper()
+                    default = self._get_default_metavar_for_optional(action)
                     args_string = self._format_args(action, default)
                     part = '%s %s' % (option_string, args_string)
 
@@ -530,7 +532,8 @@ class HelpFormatter(object):
 
     def _format_action_invocation(self, action):
         if not action.option_strings:
-            metavar, = self._metavar_formatter(action, action.dest)(1)
+            default = self._get_default_metavar_for_positional(action)
+            metavar, = self._metavar_formatter(action, default)(1)
             return metavar
 
         else:
@@ -544,7 +547,7 @@ class HelpFormatter(object):
             # if the Optional takes a value, format is:
             #    -s ARGS, --long ARGS
             else:
-                default = action.dest.upper()
+                default = self._get_default_metavar_for_optional(action)
                 args_string = self._format_args(action, default)
                 for option_string in action.option_strings:
                     parts.append('%s %s' % (option_string, args_string))
@@ -622,6 +625,12 @@ class HelpFormatter(object):
     def _get_help_string(self, action):
         return action.help
 
+    def _get_default_metavar_for_optional(self, action):
+        return action.dest.upper()
+
+    def _get_default_metavar_for_positional(self, action):
+        return action.dest
+
 
 class RawDescriptionHelpFormatter(HelpFormatter):
     """Help message formatter which retains any formatting in descriptions.
@@ -662,6 +671,22 @@ class ArgumentDefaultsHelpFormatter(HelpFormatter):
         return help
 
 
+class MetavarTypeHelpFormatter(HelpFormatter):
+    """Help message formatter which uses the argument 'type' as the default
+    metavar value (instead of the argument 'dest')
+
+    Only the name of this class is considered a public API. All the methods
+    provided by the class are considered an implementation detail.
+    """
+
+    def _get_default_metavar_for_optional(self, action):
+        return action.type.__name__
+
+    def _get_default_metavar_for_positional(self, action):
+        return action.type.__name__
+
+
+
 # =====================
 # Options and Arguments
 # =====================

Lib/test/test_argparse.py

@@ -3940,6 +3940,37 @@ class TestHelpVersionAction(HelpTestCase):
         '''
     version = ''
 
+
+class TestHelpMetavarTypeFormatter(HelpTestCase):
+    """"""
+
+    def custom_type(string):
+        return string
+
+    parser_signature = Sig(prog='PROG', description='description',
+                           formatter_class=argparse.MetavarTypeHelpFormatter)
+    argument_signatures = [Sig('a', type=int),
+                           Sig('-b', type=custom_type),
+                           Sig('-c', type=float, metavar='SOME FLOAT')]
+    argument_group_signatures = []
+    usage = '''\
+        usage: PROG [-h] [-b custom_type] [-c SOME FLOAT] int
+        '''
+    help = usage + '''\
+
+        description
+
+        positional arguments:
+          int
+
+        optional arguments:
+          -h, --help      show this help message and exit
+          -b custom_type
+          -c SOME FLOAT
+        '''
+    version = ''
+
+
 # =====================================
 # Optional/Positional constructor tests
 # =====================================

Misc/NEWS

@@ -291,6 +291,9 @@ Library
 
 - Issue #11388: Added a clear() method to MutableSequence
 
+- Issue #11174: Add argparse.MetavarTypeHelpFormatter, which uses type names
+  for the names of optional and positional arguments in help messages.
+
 Build
 -----