Iterator and Generator

2025-02-04 技术教程

# Iterator 一个对象，代表了遗传数据流，使用__next__()方法或内置函数next()# 返回连续的对象，没有数据返回时，抛出StopIteration异常# iterable 一个对象，能每次返回数据组中的一个成员 for 循环中每次返回一个值或# 内置函数iter()传入参数返回iterator对象# generator 使用了yield或者生成器表达式，申城iterator对象用一种方便的# 方法实现了iterator，在for循环取数据或使用next（）取数据

# Iterator和Generator的关系# 针对函数的列表进行优化# 针对读取大文件进行优化

def gen_num(): yield 8 yield 99 yield 999

g = gen_num()

g

<generator object gen_num at 0x0000014F3F39EC50>

next(g) # 第一次运行

---------------------------------------------------------------------------StopIteration Traceback (most recent call last)<ipython-input-12-787e36cb69a2> in <module>()----> 1 next(g) # 第一次运行StopIteration:

def gen_num2(): for i in range(8): yield i # yield有类似返回值return的效果

for g in gen_num2(): print(g) # 每次取一个值的时候，才生成这个值，节省内存

01234567

my_list = [1,2,3]

next(my_list) # 用 next方法验证是否为迭代器

---------------------------------------------------------------------------TypeError Traceback (most recent call last)<ipython-input-17-4a97765cd86f> in <module>()----> 1 next(my_list)TypeError: 'list' object is not an iterator

next(iter(my_list))

1

next(iter(my_list))

1

it = iter(my_list)next(it)

1

next(it)

2

from collections import Iterator, Iterable

isinstance(my_list, Iterator)

False

isinstance(iter(my_list), Iterator)

True

isinstance((), Iterator)

False

isinstance((), Iterable) # 元组不是迭代器，但是可迭代

True

isinstance(range(8), Iterable)

True

isinstance(range(8), Iterator)

False针对函数的列表进行优化

# Python 3:Fibonacci series up to n def fib(n): a, b = 0, 1 while a < n: print(a, end='') a, b = b, a+b print()fib(9)

0112358

def fil_list(n): a, b = 0, 1 result = [] while a < n: result.append(a) a, b = b, a+b return result

fil_list(55)

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

fil_list(1000)

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987]

def fib_gen(n): a, b = 0, 1 while a< n: yield a a, b = b, a+bfib_gen(80)

<generator object fib_gen at 0x0000014F3EA593B8>

for i in fib_gen(80): print(i)

011235813213455

[i for i in fib_gen(66)] # 列表推导式

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]针对读取大文件进行优化

import osbase_dir = r'D:\全栈\全栈资料\第三阶段 python进阶\文件与日志-演示代码\02-auto\data'log_path = os.path.join(base_dir, 'access.log')log_file = open(log_path)log_data = log_file.readlines()log_file.close()

len(log_data)

864

def read_log(log_path): with open(log_path) as f: print('Iterator:', isinstance(f, Iterator)) # open方法已经为我们生成一个迭代器 for line in f: print(line) breakread_log(log_path)

Iterator: True220.181.7.76 - - [20/May/2010:07:26:23 +0100] "GET / HTTP/1.1" 200 29460 "-" "Baiduspider+(+http://www.baidu.com/search/spider.htm)"列表推导式

[i for i in fib_gen(6)]

[0, 1, 1, 2, 3, 5]

m = [i for i in fib_gen(6)]for i in m: print(i)

011235生成器表达式

(i for i in fib_gen(5))

<generator object <genexpr> at 0x0000014F3EAC9C50>

n = (i for i in fib_gen(9))for i in n: print(i)

0112358