Python3中迭代器介绍

忘是亡心i 2022-09-09 02:07 104阅读 0赞

Python中一个可迭代对象(iterable object)是一个实现了\_\_iter\_\_方法的对象，它应该返回一个迭代器对象(iterator object)。迭代器是一个实现\_\_next\_\_方法的对象，它应该返回它的可迭代对象的下一个元素，并在没有可用元素时触发StopIteration异常。

当我们使用for循环遍历任何可迭代对象时，它在内部使用iter()方法获取迭代器对象，该迭代器对象进一步使用next()方法进行迭代。此方法触发StopIteration以表示迭代结束。

Python中大多数内置容器，如列表、元组、字符串等都是可迭代的。它们是iterable但不是iterator，把它们从iterable变成iterator可以使用iter()函数。

测试代码如下：

# reference: https://www.programiz.com/python-programming/iterator
    my_list = [1, 3, 5] # define a list
    if 0:
        my_iter = iter(my_list) # get an iterator using iter()
        print(next(my_iter)) # iterate through it using next()
        print(my_iter.__next__()) # next(obj) is name as obj.__next__()
        print(my_iter.__next__()) # 5
        #print(my_iter.__next__()) # this will raise error(StopIteration), no items left
    else: # use the for loop
        for element in iter(my_list): # 迭代器对象可以使用for语句进行遍历
            print(element, end=" ")
    
    '''
    for element in iterable:
        # do something with element
    
    Is actually implemented as:
    # create an iterator object from that iterable
    iter_obj = iter(iterable)
    while True: # infinite loop
        try:
            # get the next item
            element = next(iter_obj)
            # do something with element
        except StopIteration:
            # if StopIteration is raised, break from loop
            break
    '''
    
    # reference: https://www.geeksforgeeks.org/iterators-in-python/
    class Test:
        def __init__(self, limit):
            self.limit = limit
    
        # Creates iterator object, Called when iteration is initialized
        def __iter__(self):
            self.x = 10
            return self
    
        # To move to next element. In Python 3, we should replace next with __next__
        def __next__(self):
            # Store current value ofx
            x = self.x
    
            # Stop iteration if limit is reached
            if x > self.limit:
                raise StopIteration
    
            # Else increment and return old value
            self.x = x + 1
            return x
    
    # Prints numbers from 10 to 15
    print("\n")
    for i in Test(15):
        print(i, end=" ")
    
    print("\n")
    value = iter(Test(11))
    print(next(value))
    print(next(value))
    #print(next(value)) # raise StopIteration
    
    print("test finish")

**GitHub**：[https://github.com/fengbingchun/Python\_Test][https_github.com_fengbingchun_Python_Test]

[https_github.com_fengbingchun_Python_Test]: https://github.com/fengbingchun/Python_Test