Doc: Add output to example code in programming FAQ (pythonGH-21346)

Add output hint to document, part faq/programming, section [How do I write a function with output parameters (call by reference)?](https://docs.python.org/3/faq/programming.html#how-do-i-write-a-function-with-output-parameters-call-by-reference). This patch make the output hint just like prefix code block.

Author: zhongjiajie

Doc/faq/programming.rst

@@ -518,53 +518,56 @@ desired effect in a number of ways.
 
 1) By returning a tuple of the results::
 
- def func2(a, b):
- a = 'new-value' # a and b are local names
- b = b + 1 # assigned to new objects
- return a, b # return new values
-
- x, y = 'old-value', 99
- x, y = func2(x, y)
- print(x, y) # output: new-value 100
+ >>> def func1(a, b):
+ ...  a = 'new-value' # a and b are local names
+ ...  b = b + 1 # assigned to new objects
+ ...  return a, b # return new values
+ ...
+ >>> x, y = 'old-value', 99
+ >>> func1(x, y)
+ ('new-value', 100)
 
  This is almost always the clearest solution.
 
 2) By using global variables. This isn't thread-safe, and is not recommended.
 
 3) By passing a mutable (changeable in-place) object::
 
- def func1(a):
- a[0] = 'new-value' # 'a' references a mutable list
- a[1] = a[1] + 1 # changes a shared object
-
- args = ['old-value', 99]
- func1(args)
- print(args[0], args[1]) # output: new-value 100
+ >>> def func2(a):
+ ... a[0] = 'new-value' # 'a' references a mutable list
+ ... a[1] = a[1] + 1 # changes a shared object
+ ...
+ >>> args = ['old-value', 99]
+ >>> func2(args)
+ >>> args
+ ['new-value', 100]
 
 4) By passing in a dictionary that gets mutated::
 
- def func3(args):
- args['a'] = 'new-value' # args is a mutable dictionary
- args['b'] = args['b'] + 1 # change it in-place
-
- args = {'a': 'old-value', 'b': 99}
- func3(args)
- print(args['a'], args['b'])
+ >>> def func3(args):
+ ... args['a'] = 'new-value' # args is a mutable dictionary
+ ... args['b'] = args['b'] + 1 # change it in-place
+ ...
+ >>> args = {'a': 'old-value', 'b': 99}
+ >>> func3(args)
+ >>> args
+ {'a': 'new-value', 'b': 100}
 
 5) Or bundle up values in a class instance::
 
- class callByRef:
- def __init__(self, /, **args):
- for key, value in args.items():
- setattr(self, key, value)
-
- def func4(args):
- args.a = 'new-value' # args is a mutable callByRef
- args.b = args.b + 1 # change object in-place
-
- args = callByRef(a='old-value', b=99)
- func4(args)
- print(args.a, args.b)
+ >>> class Namespace:
+ ... def __init__(self, /, **args):
+ ... for key, value in args.items():
+ ... setattr(self, key, value)
+ ...
+ >>> def func4(args):
+ ... args.a = 'new-value' # args is a mutable Namespace
+ ... args.b = args.b + 1 # change object in-place
+ ...
+ >>> args = Namespace(a='old-value', b=99)
+ >>> func4(args)
+ >>> vars(args)
+ {'a': 'new-value', 'b': 100}
 
 
  There's almost never a good reason to get this complicated.