Iterators vs. Iterables in Python

Two features of python that help reduce the complexity of code and improve its readability are Iterators and Iterables. Although these terms sound similar, they have different meanings and functions. An Iterator is an object in Python that allows us to loop through an iterable, while an Iterable is any object that can be looped over. In this tutorial, we will take a closer look at the differences between Iterators and Iterables in Python and how they are used in coding.

What are Iterators in Python :

• An iterator is an object that can be iterated upon, meaning that you can traverse through all the values it contains.
• In Python, an iterator is an object which implements the iterator protocol, which consists of two methods :
  • __iter__() and
  • __next__(). 
• An iterator is an object that represents a stream of data. It produces one value at a time using the  next() 
• An iterator raises a  StopIteration  exception when there are no more values left to produce.
• Code Sample : 

iterator = iter([1, 2, 3])

print(next(iterator))   # Output: 1
print(next(iterator))   # Output: 2
print(next(iterator))   # Output: 3
print(next(iterator))   # Output: StopIteration

What are Iterables in Python :

• An iterable is an object that can produce an iterator using the  iter()  function.
• Examples of iterables include lists, tuples, dictionaries, and sets.
• Code Sample : 

iterable = [1, 2, 3]
iterator = iter(iterable)

print(next(iterator))   # Output: 1
print(next(iterator))   # Output: 2
print(next(iterator))   # Output: 3
print(next(iterator))   # Output: StopIteration

Iterator vs Iterable 

• An iterator is an object that represents a stream of data. An iterable is an object that can return an iterator. 
• Most of the built-in containers in Python like: list, tuple, string etc. are iterables. 
• The built-in iter() function can be used to create an iterator from an iterable:
• Code Sample : 

mylist = [1, 2, 3] 
myiter = iter(mylist) 

print(next(myiter)) 1 
print(next(myiter)) 2 
print(next(myiter)) 3 

• Code Sample : 

#creating an iterator from a list 

mylist = [1, 2, 3] 
myiter = iter(mylist) 

# traversing through the iterator 
for x in myiter: print(x) 1 2 3 

• Code Sample : 

#creating an iterator from a tuple 

mytuple = ("apple", "banana", "cherry") 
myit = iter(mytuple) 

# traversing through the iterator 
for x in myit: 
print(x) apple banana cherry 

• Code Sample : 

#creating an iterator from a string 
mystr = "banana" 
myit = iter(mystr) 

# traversing through the iterator 
for x in myit: 
print(x) 

b a n a n a

List Iterator in Python :

• A list is iterable, which means it can produce an iterator.
• A list iterator is an object that iterates through a list.
• Code Sample : 

my_list = [1, 2, 3]
print(iter(my_list))    # Output: 

Python Iterator and Iterable :

• An object is iterable if it defines the  __iter__()  method and returns an iterator object. 
• An object is an iterator if it defines both the  __iter__()  and  __next__()  methods. 
• The  __next__()  method should return the next item in the sequence or raise a  StopIteration  exception if there are no more items.
• Code Sample : 

class MyRange:
   def __init__(self, start, end):
       self.current = start
       self.end = end
   
   def __iter__(self):
       return self
   
   def __next__(self):
       if self.current >= self.end:
           raise StopIteration
       value = self.current
       self.current += 1
       return value
   
my_range = MyRange(1, 4)
for value in my_range:
   print(value)     # Output: 1, 2, 3
   
   
   

Split an Iterator from an Iterable :

• You can separate an iterator from an iterable using the  iter()  and  next()  functions.
• This allows for more control over how you interact with the iterator and the iterable.
• Code Sample : 

iterable = [1, 2, 3]
iterator = iter(iterable)

try:
   while True:
       value = next(iterator)
       print(value)
except StopIteration:
   pass