How to use the __iter__() function in Python to define the iterability of objects

How to use the __iter__() function in Python to define the iterability of an object

In Python, an iterable object refers to an object that can be traversed through an iterator . For an object to become an iterable object, its class must implement the __iter__() function. This function returns an iterator object that implements the __next__() method.

The basic format of the __iter__() function is as follows:

def __iter__(self):
    # 返回一个迭代器对象
    return self

The following is an example to demonstrate how to use the __iter__() function to define the iterability of an object.

class FibonacciSequence:
    def __init__(self, n):
        self.n = n
        self.a, self.b = 0, 1
        self.count = 0
    
    def __iter__(self):
        # 返回一个迭代器对象
        return self
    
    def __next__(self):
        if self.count < self.n:
            self.a, self.b = self.b, self.a + self.b
            self.count += 1
            return self.a
        else:
            raise StopIteration

n = int(input("请输入斐波那契数列的长度："))
fib = FibonacciSequence(n)

print("斐波那契数列前", n, "个数字为：")
for num in fib:
    print(num)

In the above example, we defined a class called FibonacciSequence to generate the Fibonacci sequence. In the class initialization method __init__(), we pass in the parameter n to represent the length of the Fibonacci sequence to be generated. The __iter__() function returns an iterator object self, and the iterator object that implements the __next__() method can be traversed using a for loop.

In the __next__() method, we use self.count to record the length of the currently generated Fibonacci sequence (that is, the number of numbers that have been returned), when self.count is less than n , we generate the next number according to the rules of the Fibonacci sequence, assign self.b to self.a, assign the sum of self.a and self.b to self.b, and add 1 to self.count. When self.count is equal to n, we throw a StopIteration exception, which is the end mark of the iterator.

Finally, in the main program, we instantiate a FibonacciSequence object fib by inputting the value of n, pass it into the for loop to traverse, and print out the first n of the Fibonacci sequence one by one number.

Through the above example, we can see how to use the __iter__() function to define the iterability of an object. As long as an object implements the __iter__() function and returns an iterator object that implements the __next__() method, you can use for loops and other methods to iterate through it. This method allows our custom objects to be traversed like Python's built-in lists, dictionaries and other objects.

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