Python-Day4 Python基础进阶之生成器/迭代器/装饰器/Json & pickle 数据序列化

>>> L = [ x*2 for x in range(5)]
>>> L
[0, 2, 4, 6, 8]
>>> g = ( x*2 for x in range(5) )
>>> g
<generator object <genexpr> at 0x000000000321EF68>

>>> next(g)
0
>>> next(g)
2
>>> next(g)
4
>>> next(g)
6
>>> next(g)
8
>>> next(g)
Traceback (most recent call last):
  File "<pyshell#11>", line 1, in <module>
    next(g)
StopIteration
>>> g
<generator object <genexpr> at 0x000000000321EF68>
>>> g = ( x*2 for x in range(5) )
>>> for n in g:
    print(n)

    
0
2
4
6
8

>>> def fib(max):
    n,a,b = 0,0,1
    while n<max:
        print(b)
        a,b =b,a+b
        n=n+1
    return ‘done‘

>>> fib(10)
1
1
2
3
5
8
13
21
34
55
‘done‘
‘‘‘仔细观察，可以看出，fib函数实际上是定义了斐波拉契数列的推算规则，可以从第一个元素开始，推算出后续任意的元素，这种逻辑其实非常类似generator。

也就是说，上面的函数和generator仅一步之遥。要把fib函数变成generator，只需要把print(b)改为yield b就可以了：

‘‘‘
>>> def fib(max):
    n,a,b = 0,0,1
    while n<max:
        yield b
        a,b =b,a+b
        n=n+1
    return ‘done‘

>>> f=fib(5)
>>> f
<generator object fib at 0x000000000321EF68>

>>> print(next(f))
1
>>> print(next(f))
1
>>> print(next(f))
2
>>> print(next(f))
3
>>> print(next(f))
5
>>> print(next(f))
Traceback (most recent call last):
  File "<pyshell#49>", line 1, in <module>
    print(next(f))
StopIteration: done

>>> for n in fib(5):
...     print(n)
...
1
1
2
3
5
‘‘‘
但是用for循环调用generator时，发现拿不到generator的return语句的返回值。如果想要拿到返回值，必须捕获StopIteration错误，返回值包含在StopIteration的value中：
‘‘‘
>>> g=fib(5)
>>> while True:
    try:
        x=next(g)
        print(‘g:‘,x)
    except StopIteration as e:
        print(‘Generator return value:‘, e.value)
        break

    
g: 1
g: 2
g: 3
g: 5
g: 8
Generator return value: done

>>> from collections import Iterable
>>> isinstance([], Iterable)
True
>>> isinstance({}, Iterable)
True
>>> isinstance(‘abc‘, Iterable)
True
>>> isinstance((x for x in range(10)), Iterable)
True
>>> isinstance(100, Iterable)
False

>>> from collections import Iterator
>>> isinstance((x for x in range(10)), Iterator)
True
>>> isinstance([], Iterator)
False
>>> isinstance({}, Iterator)
False
>>> isinstance(‘abc‘, Iterator)
False

>>> isinstance(iter([]), Iterator)
True
>>> isinstance(iter(‘abc‘), Iterator)
True

for x in [1, 2, 3, 4, 5]:
    pass

#实际上完全等价于：
# 首先获得Iterator对象:
it = iter([1, 2, 3, 4, 5])
# 循环:
while True:
    try:
        # 获得下一个值:
        x = next(it)
    except StopIteration:
        # 遇到StopIteration就退出循环
        break

def use_logging(func):
    print("%s is running" % func.__name__) #_name_获取函数的名字，也就是bar
    func()

def bar():
    print(‘i am bar‘)

use_logging(bar)

‘‘‘执行结果：
bar is running
i am bar
‘‘‘

import time
def timer(func):
    def deco():
        start_time = time.time()
        func()
        stop_time = time.time()
        print("The func run time is %s" %(stop_time-start_time))
    return deco
@timer #相当于time1=timer(time1)
def time1():
    time.sleep(1)
    print("In the time")
time1()

‘‘‘
In the time
The func run time is 1.0000569820404053
‘‘‘

import time
def timer(timeout=0):
    def decorator(func):
        def wrapper(*args,**kwargs):
            start=time.time()
            func(*args,**kwargs)
            stop=time.time()
            print ‘run time is %s ‘ %(stop-start)
            print timeout
        return wrapper
    return decorator
@timer(2)
def test(list_test):
    for i in list_test:
        time.sleep(0.1)
        print ‘-‘*20,i
  
#timer(timeout=10)(test)(range(10))
test(range(10))