The difference and relationship between iteratible objects, iterators and generators

Iteratable objects and iterators 、 The difference and connection between generators

Iteratable object

It can be used for ... in obj The traversal objects are all iteratable objects （Iterable）, There are two kinds of ：

• One is set data type , Such as list、tuple、dict、set、str etc. ;
• One is generator, Including generator and belt yield The generator function of .

So iteratable objects contain generators .

iterator

• Can be next() The object that function calls and returns the next value continuously is called an iterator ：Iterator

• Use for ... in obj Ergodic iterator , It's actually calling once iter(obj), after successively call next(obj), Until the traversal is complete

• therefore Iterators must be iterative objects

A necessary condition for judging that an object is an iterator ：

1. __iter__() The magic method returns an iterator object
2. Defined __next__() Magic methods

You can't have one without the other

generator

Generated by list , We can create a list directly . however , Limited by memory , List capacity must be limited . and , Create a containing 100 List of ten thousand elements , Not only takes up a lot of storage space , And when we only need to access the first few elements , The space occupied by most of the later elements is wasted .

Therefore, it is the best choice for us to use the generator to iterate while calculating , Although the efficiency will be reduced , for example ：

result ：

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
<generator object <genexpr> at 0x000001BE222485F0>

Generators can use next() Traverse , therefore Generators are iterators .

from collections import Iterator
y = (i for i in range(10))

print(isinstance(y, Iterator))
print(next(y))
print(next(y))
print(next(y))

result ：

True
0
1
2

summary ：

1. Iterators are iteratable objects , But iteratable objects are not necessarily iterators

2. Generators are iterators , But iterators are not necessarily generators

3. Iteratable data types list、str、dict And so on are all iterable objects Iterable But it's not an iterator Iterator, But it can go through iter(list) Function to get an iterator object

   x=iter("hjdyyds")
   print(x)
   print(next(x))
   print(next(x))
   print(next(x))
   print(next(x))
   

   result ：

   <str_iterator object at 0x0000017FA3A8CC70>
   h
   j
   d
   y
   

4. Can pass for ... in obj To traverse , Can only explain obj Is an iterable object

5. Can pass next(obj) Traverse , Can only explain obj Is the iterator

6. Determine whether it is an iterative object 、 iterator 、 General method of generator ：

   from collections import Iterable, Iterator, Generator
   x = "hjdyyds"
   print(isinstance(x, Iterable))
   print(isinstance(x, Iterator))
   print(isinstance(iter(x), Iterator))
   print(isinstance(x, Generator))
   

   result ：

   True
   False
   True
   False
   

   print(isinstance(x, Generator))

   
    result ：
   
   ```python
   True
   False
   True
   False
   

   7. If obj have access to obj[index] To visit , explain obj Is an iterable object , And it defines __getitem__() Magic methods