Unpacking operations for Python sequences and maps

Unpacking is to extract each element in a sequence or map separately. A simple way to use sequence unpacking is to extract the first or first few elements and the following elements separately, for example:

first, seconde, *rest = sequence

If there are at least three elements in sequence, then after executing the above code, first == sequence[0], second == sequence[0], rest == sequence[2:].

The function receives uncertain parameters

When the parameters of the function are uncertain, you can use *args and **kwargs. *args has no key value, and **kwargs has a key value.

#!/usr/bin/python
# -*- coding:utf-8 -*-
import sys
reload(sys)
sys.setdefaultencoding('utf-8')
  
'''
当函数的参数不确定时，可以使用*args 和**kwargs，*args 没有key值，**kwargs有key值。
  
'''
  
def fun_var_args_kwargs(data1, *args, **kwargs):
    print 'data1:', type(data1), data1
    print '*args:', type(args), args
    print '**kwargs:', type(kwargs), kwargs
  
fun_var_args_kwargs('this is data1', 2, '3', 4.0, k1='value1', k2='value2')
  
print '-------------'
  
def print_args(*args, **kwargs):
    print args.__class__.__name__, args, kwargs.__class__.__name__, kwargs
  
print_args()
print_args(1, 2, 3, a='A')

Print results:

data1: <type &#39;str&#39;> this is data1
*args: <type &#39;tuple&#39;> (2, &#39;3&#39;, 4.0)
**kwargs: <type &#39;dict&#39;> {&#39;k2&#39;: &#39;value2&#39;, &#39;k1&#39;: &#39;value1&#39;}
-------------
tuple () dict {}
tuple (1, 2, 3) dict {&#39;a&#39;: &#39;A&#39;}