优化迭代器：深入了解Python的next()函数使用方法

Python 笔记

一、next()函数使用方法介绍

#使用列表进行迭代
my_list = [4, 7, 0, 3]
#get an iterator using iter()
my_iter = iter(my_list)
#get next element using next()
#prints 4
print(next(my_iter))
#prints 7
print(next(my_iter))
 
#iterating through an entire list using next
#output : 4 7 0 3 
while True:
    try:
        print(next(my_iter))
    except StopIteration:
        break

二、next()函数产生的StopIteration异常

#using another example
numbers = [1, 2, 3]
# get an iterator using iter()
n_iter = iter(numbers)
while True:
    try:
        # get the next item
        print(next(n_iter))
    except StopIteration:
        # if StopIteration is raised, break from loop
        break

三、利用next()函数优化代码

#custom iterator
class PowTwo:

    '''Class to implement an iterator
    of powers of two'''
 
    def __init__(self, max = 0):
        self.n = 0
        self.max = max
 
    def __iter__(self):
        return self
 
    def __next__(self):
        if self.n > self.max:
            raise StopIteration
        result = 2 ** self.n
        self.n += 1
        return result

#using the custom iterator
a = PowTwo(4)
i = iter(a)
print(next(i))
print(next(i))
print(next(i))
print(next(i))
print(next(i))

四、next()函数在生成器中的应用

#generator function containing the logic to create fibonacci numbers
#the yield statement returns the next fibonacci number
def fib():
    a, b = 0, 1
    while True:
        yield a
        a, b = b, a + b
 
#using the generator
#call the fib() generator function
f = fib()
 
#using next() to recursively print the fibonacci sequence
print(next(f))
print(next(f))
print(next(f))
print(next(f))
print(next(f))

五、结论