List Builder & Builder & Iterator

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List Builder

 for  in range ()print(a)# Results [1, 2, 3, 4, 5, 6, 7, 8, 9, ten]

Above is a list builder

Insufficient: Not applicable for more data because it takes up too much memory

Generator

With list generation, we can create a list directly. However, with memory limitations, the list capacity is certainly limited. Also, creating a list of 1 million elements takes up a lot of storage space, and if we just need to access the first few elements, the vast majority of the space behind it is wasted.

So, if the list element can be calculated according to an algorithm, can we continue to calculate the subsequent elements in the process of the loop? This eliminates the need to create a complete list, which saves a lot of space. In Python, this side loop is calculated as a mechanism, called the generator: generator

Two ways to create generator:

1. Change [] to ()
2. Yield

 for  in range (+)print(a)#<generator Object <genexpr> at 0x0000000000a777d8> A is a generator object print(Next (a)) #对a进行访问 print(Next (a) ) Print (Next (a)) Print (Next (a))

#结果  1  2  3  4

For I in a: #a为生成器对象是可迭代的
    Print (i)

# Results 5 6  7 8 9 

defBar ():Print('Ok1') Count=yield1Print(count)Print('Ok2')    yield2Print('OK3')    yield3F=Bar () f.send (None)#equivalent to next (f)F.send ('eeee')#changing a variable in front of yield must first be f.send (None) to find the variable

Iterators

forThere are several types of data that can be directly acting on a loop:

A class is a collection of data types, such as,,, list tuple , and dict set str so on;

One is generator to include the generator and yield the generator function with the band.

These objects, which can be directly applied to for the loop, are called iterative objects: Iterable .

You can use to isinstance() determine whether an object is an Iterable object:

 fromCollectionsImportiterabledefBar ():Print('Ok1') Count=yield1Print(count)Print('Ok2')    yield2Print('OK3')    yield3F=Bar ()Print(Isinstance (f,iterable))#true is the corresponding data type and vice versa

Summary:

Any object that can be used for for the loop is a Iterable type;

All objects that can be used for next() functions are Iterator types, which represent a sequence of lazy computations;

Collection data types such as list , dict ,, and str so on are Iterable not Iterator , however, you can iter() get an object from a function Iterator .

 from Import  = [1,2,4= iter (l)print(type (l))print( Isinstance (l,iterator))print(isinstance (l,iterable))print(Isinstance (L, List))

List Builder & Builder & Iterator