Python Iterators

Python Iterators

An iterator is an object that contains a countable number of values. An iterator is an object that can be iterated upon, meaning that you can traverse through all the values. Technically, in Python, an iterator is an object which implements the iterator protocol, which consist of the methods __iter__() and __next__().

Iterator vs Iterable

Lists, tuples, dictionaries, and sets are all iterable objects. They are iterable containers which you can get an iterator from. All these objects have a iter() method which is used to get an iterator:

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

print(next(myit))
print(next(myit))
print(next(myit))

Looping Through an Iterator

We can also use a for loop to iterate through an iterable object:

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

for x in mytuple:
  print(x)

Create an Iterator

To create an object/class as an iterator you have to implement the methods __iter__() and __next__() to your object. The __iter__() method acts similar, you can do operations (initializing etc.), but must always return the iterator object itself. The __next__() method also allows you to do operations, and must return the next item in the sequence.

class MyNumbers:
  def __iter__(self):
    self.a = 1
    return self

  def __next__(self):
    x = self.a
    self.a += 1
    return x

myclass = MyNumbers()
myiter = iter(myclass)

print(next(myiter))
print(next(myiter))
print(next(myiter))
print(next(myiter))
print(next(myiter))