How Do Python's `__iter__` and `__next__` Methods Enable Iterator Creation?

Creating Iterators in Python

Python iterators are objects that adhere to the iterator protocol, featuring the __iter__() and __next__() methods.

iter Method:

The __iter__() method returns the iterator object, automatically invoked at the start of loops.

next Method:

The __next__() method retrieves the subsequent value and is implicitly called during loop increments. It raises a StopIteration exception when no more values are available, which is detected by loop constructs and used to cease iteration.

For instance, consider the following simplistic counter class:

class Counter:
    def __init__(self, low, high):
        self.current = low - 1
        self.high = high

    def __iter__(self):
        return self

    def __next__(self): # Python 2: def next(self)
        self.current += 1
        if self.current < self.high:
            return self.current
        raise StopIteration

When utilizing the Counter:

for c in Counter(3, 9):
    print(c)

The output will be:

3
4
5
6
7
8

Alternatively, generators offer a simpler approach to iterator creation:

def counter(low, high):
    current = low
    while current < high:
        yield current
        current += 1

Employing the generator:

for c in counter(3, 9):
    print(c)

Produces identical output. Internally, the generator resembles the Counter class, supporting the iterator protocol.

For a comprehensive overview of iterators, please refer to David Mertz's article, "Iterators and Simple Generators."

The above is the detailed content of How Do Python's `__iter__` and `__next__` Methods Enable Iterator Creation?. For more information, please follow other related articles on the PHP Chinese website!