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In [17]:

    
#https://dbader.org/blog/python-generators
#https://stackoverflow.com/questions/9884132/what-exactly-are-pythons-iterator-iterable-and-iteration-protocols

iterable is an object that it can be used in iteration (with a for loop) by using iterator

iterator is an object that define how actually do the iteration: specifically what is the next element. That's why it must have __next__ method

To support iteration an object needs to implement the iterator protocol by providing the iter and next dunder methods.

Class-based iterators are only one way to write iterable objects in Python. Also consider generators and generator expressions.



In [2]:

    
numbers = [1, 2, 3]
for n in numbers:
    print(n)



In [13]:

    
iterator=iter(numbers)



In [14]:

    
next(iterator)









    Out[14]:





1



In [10]:

    
next(iterator)









    Out[10]:





2



In [11]:

    
next(iterator)









    Out[11]:





3



In [12]:

    
next(iterator)









    



---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
<ipython-input-12-3733e97f93d6> in <module>()
----> 1 next(iterator)

StopIteration:

Iterator can be materializeted in list or tuple



In [21]:

    
iterator=iter(numbers)
list(iterator)









    Out[21]:





[1, 2, 3]



In [25]:

    
iterator=iter(numbers)
a,b,c=iterator
print(a,b,c)



In [26]:

    
iterator=iter(numbers)
max(iterator)









    Out[26]:





3



In [28]:

    
iterator=iter(numbers)
1 in iterator









    Out[28]:





True



In [15]:

    
## Class based iterator
class BoundedRepeater:
    def __init__(self, value, max_repeats):
        self.value = value
        self.max_repeats = max_repeats
        self.count = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self.count >= self.max_repeats:
            raise StopIteration
        self.count += 1
        return self.value



In [16]:

    
repeater = BoundedRepeater('Hello', 3)
for item in repeater:
    print(item)









    



Hello
Hello
Hello



In [19]:

    
repeater = BoundedRepeater('Hello', 3)
tuple(repeater)









    Out[19]:





('Hello', 'Hello', 'Hello')