How Does Python's *args and kwargs Handle Function Parameters?

Parameter Unpacking with and in Python Functions*

In Python functions, the and * syntax allows for greater flexibility in parameter handling.

Positional Argument Unpacking (kwargs)

The *args parameter collects all positional arguments as a tuple. For example:

def foo(x, y, *args):
    for a in args:
        print(a)

Calling foo(1, 2, 3) prints:

1
2
3

Keyword Argument Unpacking (kwargs)

The **kwargs parameter collects all keyword arguments as a dictionary. For example:

def bar(x, y, **kwargs):
    for k, v in kwargs.items():
        print(k, v)

Calling bar(x=1, y=2, name='John') prints:

name John

Combined Unpacking

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

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

Calling foo(123, 'a', 'b', apple='red') prints:

123 ('a', 'b') None {'apple': 'red'}

Conversely, kwargs can be used to unpack keyword arguments in function calls. For example:

def foo(a, b, c):
    print(a, b, c)

obj = {'b':10, 'c':'lee'}

foo(100, **obj) # Prints 100 10 lee

List and Tuple Unpacking with *

The * syntax can also be used to unpack lists and tuples when calling functions. For example:

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

baz = [1, 2]

foo(*baz) # Prints 1 2

Extended Iterable Unpacking

In Python 3, * can be used on the left side of an assignment to unpack iterables into individual variables. For example:

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

Positional-Only Arguments

Python 3 also introduced positional-only arguments. Functions can specify that only certain arguments can be positional. For example:

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

This function only accepts 3 positional arguments. All arguments after * must be passed as keyword arguments.

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