args and kwargs

Remarks

There a few things to note:

1. The names args and kwargs are used by convention, they are not a part of the language specification. Thus, these are equivalent:

   def func(*args, **kwargs):
       print(args)
       print(kwargs)
   #
   def func(*a, **b):
       print(a)
       print(b)
2. You may not have more than one args or more than one kwargs parameters (however they are not required)

   def func(*args1, *args2):
   #   File "<stdin>", line 1
   #     def test(*args1, *args2):
   #                      ^
   # SyntaxError: invalid syntax
   #
   def test(**kwargs1, **kwargs2):
   #   File "<stdin>", line 1
   #     def test(**kwargs1, **kwargs2):
   #                       ^
   # SyntaxError: invalid syntax
3. If any positional argument follow *args, they are keyword-only arguments that can only be passed by name. A single star may be used instead of *args to force values to be keyword arguments without providing a variadic parameter list. Keyword-only parameter lists are only available in Python 3.

   def func(a, b, *args, x, y):
       print(a, b, args, x, y)
   
   func(1, 2, 3, 4, x=5, y=6)
   #>>> 1, 2, (3, 4), 5, 6
   #
   def func(a, b, *, x, y):
       print(a, b, x, y)
   
   func(1, 2, x=5, y=6)
   #>>> 1, 2, 5, 6
4. **kwargs must come last in the parameter list.

   def test(**kwargs, *args):
   #   File "<stdin>", line 1
   #     def test(**kwargs, *args):
   #                      ^
   # SyntaxError: invalid syntax