What's the Difference Between `*args` and `kwargs` in Python Function Parameters?

Unveiling the Significance of (Double Star) and (Star) in Function Parameters*

In Python, function parameters denoted by args and *kwargs serve as versatile mechanisms to accommodate arbitrary arguments.

Unpacking Positional Arguments with *args

The *args parameter gathers all positional arguments that surpass the predefined ones into a tuple. For instance:

def foo(*args):
    for arg in args:
        print(arg)

This function can accept an arbitrary number of positional arguments, such as:

foo(1)  # Output: 1
foo(1, 2, 3)  # Output: 1 2 3

Assembling Keyword Arguments with kwargs**

On the other hand, **kwargs collects all keyword arguments into a dictionary.

def bar(**kwargs):
    for key, value in kwargs.items():
        print(key, value)

Calling this function with keyword arguments yields:

bar(name='John', age=30)  # Output: name John, age 30

Interplay of args and kwargs*

Both idioms can be combined to allow a mix of fixed and variable arguments:

def foo(kind, *args, bar=None, **kwargs):
    print(kind, args, bar, kwargs)

This function can be called as follows:

foo(123, 'a', 'b', apple='red')  # Output: 123 ('a', 'b') None {'apple': 'red'}

Additional Use Cases

• Unpacking Argument Lists: The * idiom can be used to unpack argument lists when calling a function:

def foo(bar, lee):
    print(bar, lee)

baz = [1, 2]
foo(*baz)  # Output: 1 2

• Extended Iterable Unpacking (Python 3 ): * can be used on the left side of an assignment to obtain a list:

first, *rest = [1, 2, 3, 4]
# first = 1
# rest = [2, 3, 4]

• Keyword-Only Arguments (Python 3 ): Functions can restrict keyword arguments by using the following syntax:

def func(arg1, arg2, arg3, *, kwarg1, kwarg2):
    pass

This function requires three positional arguments and any number of keyword arguments after *.

The above is the detailed content of What's the Difference Between `*args` and `kwargs` in Python Function Parameters?. For more information, please follow other related articles on the PHP Chinese website!