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Does Python support iteration?

Published in Python Iteration 3 mins read

Yes, Python fully supports iteration.

Python provides robust support for iteration, making it a fundamental aspect of the language. Iteration allows you to access elements of a sequence (like lists, tuples, strings, etc.) one by one. This capability is largely facilitated through the iterator protocol, which relies on two core methods: __iter__() and __next__().

How Iteration Works in Python

  • Iterable: An object capable of returning its members one at a time. Common examples include lists, tuples, strings, dictionaries, and sets.
  • Iterator: An object that produces successive items from the iterable. An iterator is created from an iterable using the iter() function. The iterator's __next__() method retrieves the next item. When there are no more items, __next__() raises a StopIteration exception.
  • The for loop: Python's for loop is a key mechanism for iteration. It automatically handles the process of obtaining an iterator from an iterable and repeatedly calling the iterator's __next__() method until a StopIteration exception is raised.

The Iterator Protocol

To support iteration, an object must adhere to the iterator protocol, which involves implementing the following methods:

  • __iter__(): This method should return the iterator object itself. It is called at the beginning of a loop.
  • __next__(): This method should return the next value from the iterator. When there are no more values to return, it should raise a StopIteration exception.

Example

my_list = [1, 2, 3]
my_iterator = iter(my_list)

print(next(my_iterator))  # Output: 1
print(next(my_iterator))  # Output: 2
print(next(my_iterator))  # Output: 3

# Attempting to call next() again will raise StopIteration
# print(next(my_iterator))

In this example, my_list is an iterable. Calling iter(my_list) returns an iterator object. Each call to next() retrieves the next element.

Pythonic Iteration with for Loops

The for loop provides a cleaner and more Pythonic way to iterate:

my_list = [1, 2, 3]

for item in my_list:
    print(item)

This loop automatically handles the iterator creation and exception handling.

Conclusion

Python's support for iteration is a cornerstone of the language's design, providing a flexible and efficient way to process sequences of data. The iterator protocol, along with features like for loops, makes iteration easy and intuitive.

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