Python Basics 13-iterators and generators

Iterators and generators

 any value that can be used for a loop is an iterative 
 Iterative protocol: 
 Internally containing the __iter__ method is an iterative 
 iterator protocol 
 that contains both the __iter method and the __next__ method are iterators 
 What is iterator 
 iterator =iter (iterative). Bring a __next__ method 
 Advantage: Save memory \ Fast 
 Properties: Lazy Operation 
 Common: list \ dictionary \ element \ string \ collection \range\ file handle \enumerat e 
 Range Differences in Python 2 and Python3 
 python2x range No matter what range, a list is generated that will be used to store all values 
 Python3, regardless of range,            Doesn't actually generate heat. A value of 
 Python3, with the yield from 
 Generator function: 
 Any function with yield is a generator function; 
            The call to the generator function does not trigger the execution of the code, but instead returns a generator, wants the generator function to execute, uses next () 
 to record the current location, and waits for 
 How to take the value from the generator? 
        1) Next can be stopped at any time, the last time it will error 
 2) for loop, traversal from beginning to end, do not encounter Break\return does not stop 
 3) list\tuple data type cast 
        The simple method of yield return value, if itself is the loop of an iterative, and to the iteration of the data is not an element in return, you can use the yield from the 
 when using send, after the generator created by the need for pre-activation, can be implemented with adorners. 
 A generator is used to solve the decoupling of memory problems and program functions 
 List derivation: 
 [I for I in rang () if i%3==0] 
 Generator expression 
 (I for I in rang () if i%3==0) 
 A generator can only be taken once 
 the generator does not find him to be worth the time, not the value. 

Python basic 13-iterators and generators