在python中使用迭代器？

我刚刚学习了Python中的迭代器，但是我很难实现它们

我正在尝试编写一个类，以使此循环工作：

  odds = OddNumbers(13)
  for i in odds:
      print(i) 

我想写一个iter（）函数和一个next（）函数来实现这一点

到目前为止，我已经：

class OddNumbers:

    def __init__(self, number):
        self.number = number

    def __iter__(self):
        return self

    def __next__(self):
        current = self.number
        if self.number%2 == 0:
            return current
        else:
            raise StopIteration

但目前这一切都没有回报。我希望输出是

1
3
5
7
9
11
13

---

帮助？

您的对象需要跟踪其状态，并在调用

\uuuu next\uuuu

时对其进行更新

class OddNumbers(object):
    def __init__(self, number):
        self.current = ...
        self.number = number

    def __iter__(self):
        return self

    def __next__(self):
        # Update self.current
        # If the limit has been reached, raise StopIteration
        # Otherwise, return something

---

您需要另一个变量来跟踪当前编号：

def __init__(self, number):
    self.number = number
    self.current = 1

然后，您需要将其与结束数字进行比较，并可能增加它：

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

---

可能有一种更干净的方法可以做到这一点，但这里有一个简单的方法：

class OddNumbers:

    def __init__(self, number):
        self.number = number

    def __iter__(self):
        self.current = self.number
        return self

    def __next__(self):
        if self.current > 0:
            if self.current % 2 == 0:
                self.current -= 1
            self.current -= 1
            return self.current + 1
        raise StopIteration

---

这将为您提供一个类似迭代器的对象，它提供偶数或奇数。但是，它不能满足for循环语义，因为它不是真正的迭代器

class NumberIterator(object):
    """Returns simple even/odd number iterators."""
    def __init__(self, current):
        self.current = current
    def next(self):
        self.current += 2
        return self.current
    @classmethod
    def getOddIterator(cls):
        return cls(-1) # start at 1
    @classmethod
    def getEvenIterator(cls):
        return cls(0) # start at 2


    odd_numbers = NumberIterator.getOddIterator()
    even_numbers = NumberIterator.getEvenIterator()

    odd_numbers.next() # Returns 1
    odd_numbers.next() # Returns 3

---

你想干什么？您只有一个元素。为什么需要将该类设置为iterable？示例代码应该打印哪些数字？如果以奇数开头，则

\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu。如果以偶数开头，它将只返回该数字。你的意思是让
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu！不过我现在已经编辑了它。在您的情况下，
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
将在第一个循环中引发异常，因此迭！这解决了我的问题！在某个阶段，我确实有另一个变量来跟踪迭代次数，除了我没有用init方法初始化它，我只是在下一个阶段引入了它。再次感谢你！你不应该把全部答案告诉OP，这并不能教会他们任何东西。@augurar，OP表现出了努力，并发布了真实的代码，所以答案是正确的。评论显示他从中吸取了教训。@BrentWashburne你刚刚告诉了他答案。所以他知道了正确的答案。干得好，我想。