Python Iterators Tutorial With Example

Python iterator is an object that “implements the iterator protocol, which consists of the methods __iter__() and __next__()”.

Iterators loop over a collection of items, such as lists, tuples, dictionaries, or sets, one element at a time. They allow you to traverse a collection in a memory-efficient way because they do not load all elements into memory at once but rather generate each element on-the-fly when you request it.

You can create an iterator object from an iterable (e.g., lists, tuples, dictionaries, sets, or strings) using the built-in “iter()” function.

To get the next item from the iterator, you use the built-in “next()” function.

When there are no more items left to return, the iterator raises a StopIteration exception.

Example

main_list = [1, 2, 3, 4]

# Create an iterator object from the list
main_iterator = iter(main_list)

# Iterate over the elements using the iterator
print(next(main_iterator))
print(next(main_iterator))
print(next(main_iterator))
print(next(main_iterator))

# Raises StopIteration exception
print(next(main_iterator))

Output

1
2
3
4

Traceback (most recent call last):
File "/Users/krunallathiya/Desktop/Code/pythonenv/env/app.py", line 13, in <module>
print(next(main_iterator))

StopIteration

You can also loop over an iterable using a for loop, which automatically creates and handles the iterator for you:

main_list = [1, 2, 3, 4]

# The for loop automatically creates and uses an iterator to loop over
for item in main_list:
  print(item)

Output

To create your own custom iterator, you can define a class that implements the __iter__() and __next__() methods:

class MyRange:
  def __init__(self, start, end):
    self.start = start
    self.end = end

  def __iter__(self):
    return self

  def __next__(self):
    if self.start >= self.end:
      raise StopIteration
    else:
      current = self.start
      self.start += 1
      return current


# Create a custom iterator that generates numbers from 1 to 4
main_range = MyRange(1, 5)

# Iterate over the numbers using a for loop
for number in main_range:
  print(number)

Output

This example demonstrates creating a custom iterator that generates numbers in a specified range.

Python Iterators

Example

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