Issue #16933 (2.7 forward-port): Improve choices examples in argparse docs.

Doc/library/argparse.rst

@@ -1003,32 +1003,33 @@ choices
 ^^^^^^^
 
 Some command-line arguments should be selected from a restricted set of values.
-These can be handled by passing a container object as the ``choices`` keyword
+These can be handled by passing a container object as the *choices* keyword
 argument to :meth:`~ArgumentParser.add_argument`.  When the command line is
-parsed, argument values will be checked, and an error message will be displayed if
-the argument was not one of the acceptable values::
-
-   >>> parser = argparse.ArgumentParser(prog='PROG')
-   >>> parser.add_argument('foo', choices='abc')
-   >>> parser.parse_args('c'.split())
-   Namespace(foo='c')
-   >>> parser.parse_args('X'.split())
-   usage: PROG [-h] {a,b,c}
-   PROG: error: argument foo: invalid choice: 'X' (choose from 'a', 'b', 'c')
-
-Note that inclusion in the ``choices`` container is checked after any type_
-conversions have been performed, so the type of the objects in the ``choices``
+parsed, argument values will be checked, and an error message will be displayed
+if the argument was not one of the acceptable values::
+
+   >>> parser = argparse.ArgumentParser(prog='game.py')
+   >>> parser.add_argument('move', choices=['rock', 'paper', 'scissors'])
+   >>> parser.parse_args(['rock'])
+   Namespace(move='rock')
+   >>> parser.parse_args(['fire'])
+   usage: game.py [-h] {rock,paper,scissors}
+   game.py: error: argument move: invalid choice: 'fire' (choose from 'rock',
+   'paper', 'scissors')
+
+Note that inclusion in the *choices* container is checked after any type_
+conversions have been performed, so the type of the objects in the *choices*
 container should match the type_ specified::
 
-   >>> parser = argparse.ArgumentParser(prog='PROG')
-   >>> parser.add_argument('foo', type=complex, choices=[1, 1j])
-   >>> parser.parse_args('1j'.split())
-   Namespace(foo=1j)
-   >>> parser.parse_args('-- -4'.split())
-   usage: PROG [-h] {1,1j}
-   PROG: error: argument foo: invalid choice: (-4+0j) (choose from 1, 1j)
-
-Any object that supports the ``in`` operator can be passed as the ``choices``
+   >>> parser = argparse.ArgumentParser(prog='doors.py')
+   >>> parser.add_argument('door', type=int, choices=range(1, 4))
+   >>> print(parser.parse_args(['3']))
+   Namespace(door=3)
+   >>> parser.parse_args(['4'])
+   usage: doors.py [-h] {1,2,3}
+   doors.py: error: argument door: invalid choice: 4 (choose from 1, 2, 3)
+
+Any object that supports the ``in`` operator can be passed as the *choices*
 value, so :class:`dict` objects, :class:`set` objects, custom containers,
 etc. are all supported.