学ぶ Building Custom Iterators | Understanding Iterators

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To fully understand iterators in Python, you need to know how to build your own custom iterator classes. When you design a custom iterator, you must implement two special methods: __iter__ and __next__. The __iter__ method should return the iterator object itself, while the __next__ method is responsible for returning the next item in the sequence. If there are no more items to return, __next__ should raise the StopIteration exception to signal the end of the iteration. Managing the internal state of your iterator is crucial, as it allows you to keep track of where you are in the sequence. This is typically done by storing a variable, such as a counter, within the iterator object. Each time __next__ is called, you update this variable and determine whether to return the next value or to raise StopIteration.


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class EvenNumbers:
    def __init__(self, limit):
        self.limit = limit
        self.current = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self.current > self.limit:
            raise StopIteration
        result = self.current
        self.current += 2
        return result

# Usage:
even_iter = EvenNumbers(10)
for number in even_iter:
    print(number)

1. When should a custom iterator's `next` method raise the `StopIteration` exception?

2. Which of the following statements describe the differences between `iter` and `next` in custom iterators?

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セクション 1. 章 2

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セクション 1. 章 2

Building Custom Iterators

1. When should a custom iterator's __next__ method raise the StopIteration exception?

2. Which of the following statements describe the differences between __iter__ and __next__ in custom iterators?

1. When should a custom iterator's `next` method raise the `StopIteration` exception?

2. Which of the following statements describe the differences between `iter` and `next` in custom iterators?