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Python | Difference between iterable and iterator

  • Difficulty Level : Easy
  • Last Updated : 23 Aug, 2019

Iterable is an object, which one can iterate over. It generates an Iterator when passed to iter() method. Iterator is an object, which is used to iterate over an iterable object using __next__() method. Iterators have __next__() method, which returns the next item of the object.

Note that every iterator is also an iterable, but not every iterable is an iterator. For example, a list is iterable but a list is not an iterator. An iterator can be created from an iterable by using the function iter(). To make this possible, the class of an object needs either a method __iter__, which returns an iterator, or a __getitem__ method with sequential indexes starting with 0.

Code #1 :

for city in ["Berlin", "Vienna", "Zurich"]:
for city in ("Python", "Perl", "Ruby"):
for char in "Iteration is easy":
    print(char, end = " ")

Output :



I t e r a t i o n   i s   e a s y 

When a for loop is executed, for statement calls iter() on the object, which it is supposed to loop over. If this call is successful, the iter call will return an iterator object that defines the method __next__(), which accesses elements of the object one at a time. The __next__() method will raise a StopIteration exception, if there are no further elements available. The for loop will terminate as soon as it catches a StopIteration exception.
Let’s call the __next__() method using the next() built-in function.

Code #2 : Function ‘iterable’ will return True, if the object ‘obj’ is an iterable and False otherwise.

# list of cities
cities = ["Berlin", "Vienna", "Zurich"]
# initialize the object
iterator_obj = iter(cities)

Output :


Note: If ‘next(iterator_obj)’ is called one more time, it would return ‘StopIteration’.

Code #3 : Check object is iterable or not

# Function to check object
# is iterable or not 
def iterable(obj):
        return True
    except TypeError:
        return False
# Driver Code     
for element in [34, [4, 5], (4, 5),
             {"a":4}, "dfsdf", 4.5]:
    print(element, " is iterable : ", iterable(element))

Output :

34  is iterable :  False
[4, 5]  is iterable :  True
(4, 5)  is iterable :  True
{'a': 4}  is iterable :  True
dfsdf  is iterable :  True
4.5  is iterable :  False

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