Arbitrary number of positional arguments:

Defining a function capable of taking an arbitrary number of arguments can be done by prefixing one of the arguments with a \\*

def func(*args):
    # args will be a tuple containing all values that are passed in
    for i in args:
        print(i)

func(1, 2, 3)  # Calling it with 3 arguments
# Out: 1
#      2
#      3

list_of_arg_values = [1, 2, 3]
func(*list_of_arg_values)  # Calling it with list of values, * expands the list
# Out: 1
#      2
#      3 

func()  # Calling it without arguments
# No Output

You can’t provide a default for args, for example func(*args=[1, 2, 3]) will raise a syntax error (won’t even compile).

You can’t provide these by name when calling the function, for example func(*args=[1, 2, 3]) will raise a TypeError.

But if you already have your arguments in an array (or any other Iterable), you can invoke your function like this: func(*my_stuff).

These arguments (*args) can be accessed by index, for example args[0] will return the first argument

Arbitrary number of keyword arguments

You can take an arbitrary number of arguments with a name by defining an argument in the definition with two \\* in front of it:

def func(**kwargs):
    # kwargs will be a dictionary containing the names as keys and the values as values
    for name, value in kwargs.items():
        print(name, value)

func(value1=1, value2=2, value3=3)   # Calling it with 3 arguments
# Out: value1 1
#      value2 2
#      value3 3

func()                               # Calling it without arguments
# No Out put

my_dict = {'foo': 1, 'bar': 2}
func(**my_dict)                      # Calling it with a dictionary
# Out: foo 1
#      bar 2

You can’t provide these without names, for example func(1, 2, 3) will raise a TypeError.

kwargs is a plain native python dictionary. For example, args['value1'] will give the value for argument value1. Be sure to check beforehand that there is such an argument or a KeyError will be raised.

Warning

You can mix these with other optional and required arguments but the order inside the definition matters.

The positional/keyword arguments come first. (Required arguments).

Then comes the arbitrary *arg arguments. (Optional).

Then keyword-only arguments come next. (Required).

Finally the arbitrary keyword **kwargs come. (Optional).

#       |-positional-|-optional-|---keyword-only--|-optional-|
def func(arg1, arg2=10 , *args, kwarg1, kwarg2=2, **kwargs):
     pass