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Inside the English website come from the python developers guide PEP 448 – Additional Unpacking Generalizations | Python.org

This article mainly introduces * and ** to launch a detailed introduction.

Unpacking is proposed to be allowed inside tuple, list, set, and dictionary displays.

Unpacking operations can be applied to tuples, lists, collections, and dictionaries.

I’ll start with a review of range and its use to generate tuples, lists, and collections.

li = list(range(7))
print(li)
tu = tuple(range(7))
print(tu)
se = set(range(7))
print(se)
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[0, 1, 2, 3, 4, 5, 6]
(0, 1, 2, 3, 4, 5, 6)
{0, 1, 2, 3, 4, 5, 6}
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Available position

* and ** can be used to unpack anywhere.

Specifically, in function calls, in comprehensions and generator expressions, and in displays.

display

The so-called for display I think is direct output, (total can not be direct output 😶).

li = list(range(7))
tu = tuple(range(7))
se = set(range(7))

print(*li,*tu,*se)

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Unpack lists, tuples, and collections directly.

Print (**{“name”:” Sian “,”name”:25}) SyntaxError: invalid syntax

Although not used for direct output, it can be sliced.

dic = {"name":"sian"."name2":"sian"}
a = {'a':0,**dic,'c':1}

print(a)
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{'a':0,"name":"sian","name2":"sian",'c':1}
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** can be sliced, so can * :

li = [1.2.3]
a = [1,*li,0]

print(a)

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[1, 1, 2, 3, 0]
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The generator derivation is:

print(i for i in range(7))
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<generator object <genexpr> at 0x000002502D43A510>
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The output tells you that this is a generator object.

You can create lists and collections with generator objects, but you cannot create tuples directly.

li = [i for i in range(7)]
se = {i for i in range(7)}
print(li,se)
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[0, 1, 2, 3, 4, 5, 6] {0, 1, 2, 3, 4, 5, 6}
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Unpacking generator objects with * is:

print(*[i for i in range(7)])
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Just omit variable names :clap:.

It’s very common for function calls.

def function(num,*args) :
    print(num)
    print(args)
    print(*args)
    
function(1.2.3.4.5.6.7)
function('a'.1.2.3.'b')
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1
(2, 3, 4, 5, 6, 7)
2 3 4 5 6 7
a
(1, 2, 3, 'b')
1 2 3 b
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* ARGS is used to receive arguments of arbitrary length and pack them up and store them in tuples.

But the position is not flexible enough, it will take all the arguments from the *args starting position to the end.

Def function(first,*args,last): function() missing 1 required keyword-only argument: ‘last’

But you can manually specify parameters to solve this problem. For example, you force a value for last like this.

def function(first,*args,last="c") :
    print("first:",first)
    print(args)
    print("last:",last)

function(1.2.3.4.5.6.7)
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first: 1
(2, 3, 4, 5, 6, 7)
last: c
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* Parameters before args cannot be specified manually.

def function(first='a',*args) :
    print("first:",first)
    print(args)
    
function(1.2.3.4.5.6.7)
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first: 1
(2, 3, 4, 5, 6, 7)
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Take a look at the ** receiving argument and package it as a dictionary.

def function(first='a',**kwargs) :
    print("first:",first)
    print(kwargs)
    
function(1,name = "Sian", age = 25,b=2)
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first: 1
{'name': 'Sian', 'age': 25, 'b': 2}
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The position of the argument list is the same as that of *. SyntaxError: invalid syntax. But the preceding arguments can be specified.