1.17 Python Basics-iterators and generators first knowledge

An object that can iterate is called an iterative object, and an iterator and a generator function are iterative objects.

List Resolution Expressions: You can easily and efficiently process an iterative object and generate a list of results

Example code:

 for  in range ()# output [0,1,4,9,16,25,36,49,64,81]

Builder expression: A generator can be returned quickly and easily. The syntax and list parsing of the builder expression is basically the same, except that [] is replaced by ()

The generator's data is generated only when it is called

Example code:

 for  in range ()print(a)#  output, print the Generator object address <generator Object <genexpr> at 0x000001a4118978e0>

Call Method 1:

Print# equivalent to print (a.__next__ ())

Call Method 2:

For I in A:    print (i)

Call Method 3:

 while True:     Try :         Print (Next (a))     except stopiteration:          Break

　　

Generator functions

Example code:

deffib (): A, B= 0,1 whiletrue:a,b= b,a+byieldbPrint(FIB ()) forFinchfib ():ifF < 1000:        Print(f)Else:         Break#Output Results<generator Object fib at 0x0000024f66a478e0>123581321345589144233377610987

Iterative and Iterative objects:

1, can iterate object: iterable

Series objects are iterative objects, and generator functions and generator expressions are also iterative objects.

Determine if an iterative object is being tested through the methods in the collections module, for example:

Import for in range (123print(isinstance (a,collections). iterable))print(isinstance (b,collections. iterable))#  output result TrueFalse

2, Iterators: Iterator

You can use the built-in function next (), call the iterator's __next__ () method, and then return to the next item value object is the iterator

Import= [1,2,3,4]print(isinstance (b,collections. iterable))print(isinstance (b,collections. Iterator)#  output result, B is an iterative object, but not an iterator truefalse

Like lists, dictionaries, tuples are iterative objects, but not iterators, we can use the built-in function iter () to convert to an iterator, the sample code:

Import= [1,2,3,4]print(isinstance (b,collections. iterable))print(isinstance (b,collections. Iterator))print(Isinstance (ITER (b), collections. Iterator))#  output result truefalsetrue

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1.17 Python Basics-iterators and generators first knowledge