Python concept decorator, iterator, generator

Decorators, iterators, generators are all functional knowledge categories

1. Decorative Device

To understand the adorner, first understand the closure function.

closure function : 1, defines the function inside the function;

2. The function body code of the function contains a reference to the name of the outer scope (not the global scope);

3. The closure function is usually returned with return, which can then be called arbitrarily.

Eg: inner () is the closure function in the following code

def outer ():
    X=1
    def inner ():
        Print (x)
    return inner
F=outer ()

Adorner: that is, the application of a closure function.

What is an adorner? : A device that decorates its human being can be any callable object, or an adorner can be any callable object.

Adorner principle: 1, do not modify the source code of the Decorated object 2, do not modify the calling method of the decorated object
Object of the adorner: Add new features to the adorned object, following the 1 and 2 prerequisites

Import TimedefTimmer (func):definner (): Start=time.time () Res=func () Stop=time.time ()Print('run time is%s'% (stop-start)) returnResreturnInner@timmer#Index=timmer (Index)defindex (): Time.sleep (1)    Print('Welecome to index')    return1111Res=index ()Print(RES)

2. iterators

Iterators : iterators are tools that iterate.

What is an iteration? : Refers to a repeating process, each repetition is called an iteration, and the result of each repetition is the initial value of the next repetition

Why do we have iterators? : For sequence type: Str,list,tuple, you can rely on the index to iterate over the value, but for Dict,set, the file, Python must provide us with an iterative way of not relying on the index-the iterator

What is an iterative object? : An iterative object refers to an object with a built-in __iter__ method, that is, obj.__iter__, as follows

' Hello '. __iter__
(__iter__).
[1,2,3].__iter__
{' A ': 1}.__iter__
{' A ', ' B '}.__iter__
Open (' A.txt '). __iter__

What is an iterator object? : An iterator object is the result of an iterative object execution obj.__iter__ (), whereas an Iterator object refers to an object that has a built-in __iter__ and built-in __next__ method.

The file type is an iterator object:
Open (' A.txt '). __iter__ ()
Open (' A.txt '). __next__ ()

Note: An iterator object must be an iterative object, and an iterative object is not necessarily an iterator object.

eg

b=='name':'Lili',' Age':' -','Sex':'male'}d_iter=iter (d)#D_iter=iter (d) whileTrue:Try:        Print(Next (d_iter))exceptstopiteration: Break

Advantages:
Provides a unified, index-independent way to take a value
Iterators have only one value in memory at the same time, saving more memory
Disadvantages:
Can only be taken back, and it is disposable.
Cannot count the number of values, that is, the length

3. Generator

What is a generator? : As long as the yield keyword appears in the function body, then executing the function will not execute the function code, you will get a result, the result is the generator

Generators are iterators

deffunc ():Print('=====>1')    yield1Print('=====>2')    yield2Print('=====>3')    yield3g=func ()#g.__iter__res1=Next (g)Print(res1) Res2=Next (g)Print(res2) Res3=Next (g)Print(RES3)

Yield Features:
1, yield provides us with a way to customize the iterator object
2. The difference between yield and return 1:yield can return multiple values #2: The state that the function is paused and resumed is saved by yield.

Python concept decorator, iterator, generator