Python iterators and generators

One, iterator

an iterative object is now known: str list tuple dict set range and file handle.

But what is an iterative object? The method of measurement for an iterative object.

Method One: Dir (the object being measured) if he contains __iter__, then this object is called an iterative object.

The following string s is an iterative object:

s= ' abcdef ' Print (' __iter__ ' in Dir (s))

can iterate over objects, what does iterable have to do with iterators? An iterative object can be converted to an iterator ( an iterative object. __iter__ ()).

S1 = s.__iter__ () print (S1) #iterator  follows the iterator protocol

The value of the iterator: (iterator. __next__ ())

#迭代器取值: S2 = ' ABCD ' s3 = s2.__iter__ () print (s3.__next__ ())   #aprint (s3.__next__ ())   #b

Data that contains only the __iter__ method is an iterative object that contains the __iter__ method, and the data that contains the __next__ method is an iterator

#迭代器的判断: The data that has the __iter__ method and contains the __next__ method is the iterator L = [1,2,3,4]print (' __iter__ ' in Dir (l))  #Trueprint (' __next__ ' in Dir (l ))  #Falseliter = l.__iter__ () print (' __next__ ' in Dir (Liter))  #Trueprint (liter.__next__ ())     #1print ( Liter.__next__ ())     #2print (liter.__next__ ())     #3print (liter.__next__ ())     #4

　Method Two: Measure whether he is an iterator or an iterator:

# method Two Tests whether he is an iterator or an iterator object L = [1,2,3]l_iter = l.__iter__ () from collections import Iterablefrom collections Import Iteratorprint ( Isinstance (l,iterable))      #Trueprint (Isinstance (l,iterator))      #Falseprint (Isinstance (l_iter,iterator)) # Trueprint (Isinstance (l,list))          #Truedied　　

　The meaning of iterators:

1), iterators save memory.
2), the iterator inertia mechanism.
3), iterators can not be repeated, always down execution.

Internal mechanism for the For loop:

1), internal contains the __iter__ method, he will be iterative objects first into an iterator.
2), and then call the __next__ method.
3), the For loop has an exception handling method.　

#用迭代器来表示for循环的内部机制for I in [N/a]:    print (i) L = [1,2,3]l_iter = l.__iter__ () while True:    try:        print (L_iter . __next__ ())    except stopiteration:        break

　Second, generator

　

　

Python iterators and generators