Iterator and Generator

# Iterator  一個(gè)對(duì)象，代表了遺傳數(shù)據(jù)流，使用__next__()方法或內(nèi)置函數(shù)next()
# 返回連續(xù)的對(duì)象，沒(méi)有數(shù)據(jù)返回時(shí)，拋出StopIteration異常

# iterable  一個(gè)對(duì)象，能每次返回?cái)?shù)據(jù)組中的一個(gè)成員  for 循環(huán)中每次返回一個(gè)值 或
# 內(nèi)置函數(shù)iter()傳入?yún)?shù)返回iterator對(duì)象

# generator  使用了yield或者生成器表達(dá)式，申城iterator對(duì)象  用一種方便的
# 方法實(shí)現(xiàn)了iterator，在for循環(huán)取數(shù)據(jù)或使用next（）取數(shù)據(jù)

# Iterator和Generator的關(guān)系
# 針對(duì)函數(shù)的列表進(jìn)行優(yōu)化
# 針對(duì)讀取大文件進(jìn)行優(yōu)化

def gen_num():
    yield 8
    yield 99
    yield 999

g = gen_num()

g

<generator object gen_num at 0x0000014F3F39EC50>

next(g) # 第一次運(yùn)行

---------------------------------------------------------------------------

StopIteration                             Traceback (most recent call last)

<ipython-input-12-787e36cb69a2> in <module>()
----> 1 next(g) # 第一次運(yùn)行

StopIteration: 

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

for g in gen_num2():
    print(g)  # 每次取一個(gè)值的時(shí)候，才生成這個(gè)值，節(jié)省內(nèi)存

0
1
2
3
4
5
6
7

my_list = [1,2,3]

next(my_list)  # 用 next方法驗(yàn)證是否為迭代器

---------------------------------------------------------------------------

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)  # 元組不是迭代器，但是可迭代

True

isinstance(range(8), Iterable)

True

isinstance(range(8), Iterator)

False

針對(duì)函數(shù)的列表進(jìn)行優(yōu)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)

0
1
1
2
3
5
8

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+b

fib_gen(80)

<generator object fib_gen at 0x0000014F3EA593B8>

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

0
1
1
2
3
5
8
13
21
34
55

[i for i in fib_gen(66)]  # 列表推導(dǎo)式

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

針對(duì)讀取大文件進(jìn)行優(yōu)化

import os
base_dir = r'D:\全棧\全棧資料\第三階段 python進(jìn)階\文件與日志-演示代碼\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方法已經(jīng)為我們生成一個(gè)迭代器
        for line in f:
            print(line)
            break

read_log(log_path)

Iterator: True
220.181.7.76 - - [20/May/2010:07:26:23 +0100] "GET / HTTP/1.1" 200 29460 "-" "Baiduspider+(+http://www.baidu.com/search/spider.htm)"

列表推導(dǎo)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)

0
1
1
2
3
5

生成器表達(dá)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)

0
1
1
2
3
5
8