Python variable length parameter detailed explanation

If you want a function to receive arbitrarily multiple parameters, you can use variable-length parameters.

Two basic forms of variable length parameters¶

There are two variable length parameters in python custom functions. 

1. *args: The first is *XXX. When passing in additional parameters, you can pass in the parameter value directly without specifying the parameter name. 
2. *kargs: The second type is **XXX This type returns a dictionary. You need to specify the parameter name when you pass it in.

Added an asterisk * Variable length parameters will be imported in the form of tuples, storing all unnamed variable parameters. 

The parameters with two asterisks ** will be imported in the form of a dictionary to store the named variable parameters.

example¶

#coding=utf-8

#The first one is the tuple form, the second is the dictionary form
def sun(*a, **b):
    print(a)
    print(b)

sun(1, 55258, x=25412, y=5123512)

output

(1,55258)
{'x':25412,'y':5123512}

Usage¶

Example 1¶

A simple example of variable-length parameters, the first is a normal parameter, the second is a variable-length parameter, we can print out in turn, the variable-length parameter is in the form of a tuple, such as b represents (55258,25412,5123512), and As a common parameter, a can only represent the first 1.

#coding=utf-8

#Indefinite length parameter simple example, the first is a normal parameter, the second is an indefinite length parameter
def sun(a, *b):
    print(a)
    print(b)

sun(1,55258,25412,5123512)

output:

1
(55258, 25412, 5123512)

Example 2¶

When a, *b, **c appear at the same time, as follows:

#coding=utf-8

#Use variable length parameters to pass fixed values, note that b and c can be omitted, and a cannot be omitted
def fuzhi(a, *b, **c):
    print(a)
    print(b)
    print(c)
fuzhi(853521, 65134, 635263, 45563, 365, x=99, y=999)

output:

853521
(65134,635263,45563,365)
{'x':99, 'y':999}

a common parameter a cannot be omitted, if we omit a

#coding=utf-8

#Use variable length parameters to pass fixed values, note that b and c can be omitted, and a cannot be omitted
def fuzhi(a, *b, **c):
    print(a)
    print(b)
    print(c)
fuzhi()

error prompt:

TypeError: fuzhi() missing 1 required positional argument: 'a'

Example 3¶

When we use variable length parameters to accumulate:

#coding=utf-8

#Accumulate with variable length parameters
print(1, 2, 3, 4, 5)

def sum(*nums):
    """
    Find the sum of multiple numbers
     :param list_one: receives the variable length parameter of the number, will assemble the parameter into a tuple, and assign it to the variable length parameter
     :return: return the sum of all numbers
    """
    result = 0
    for num in nums:
        if isinstance( num, (int,float)):
           result = result + num

    return result

sum()

output:

1 2 3 4 5
6

Example 4¶

When we write the ordinary parameter in the variable length parameter and write it in the back

#coding=utf-8

def JayChou(a, *b, c):
    print(a)
    print(b)
    print(c)
JayChou(1, 555, 5768, 55451)

operation result
The following error will appear, so the position cannot be changed at will

TypeError: JayChou() missing 1 required keyword-only argument: 'c'

Example 5¶

If no parameters are specified when the function is called, it is an empty tuple. We can also not pass unnamed variables to the function

#coding=utf-8

# If no parameters are specified in the function call, it is an empty tuple. We can also not pass unnamed variables to the function.
def void_tuple(a, *tuplela):
    print(a)
    for b in tuplela:
        print(b)
    return

print(1)
print(2, 3, 4, 5)

output:

1
2 3 4 5