python中的迭代器,生成器與裝飾器詳解

# 對list進行for循環本質上是調用瞭list的迭代器
list = [1,2,3,4]

# for 循環調用
for elem in list:
    print(elem)

# 迭代器調用
list_iter = list.__iter__()
while True:
   try:
    print(next(list_iter)) 
   except StopIteration:
       break

# 可迭代對象類
class CountDown(object):
    def __init__(self,num):
        self.num = num
    def __iter__(self):
        return MyIterator(self.num)

# 迭代類
class MyIterator(object):
    def __init__(self,num):
        self.NUM= num
        self.FINAL = 0
        self.now = num
        
    def __iter__(self):
        return self
    
    def __next__(self):
        step = 1 if self.NUM<self.FINAL else -1
        while self.now != self.FINAL:
            self.now += step
            return self.now - step
        raise StopIteration
        
cd_pos = CountDown(5)
cd_neg = CountDown(-5)
for i,j in zip(cd_pos,cd_neg):
    print(f'pos:{i}\tneg:{j}')

from  collections import Iterable
def f():
    pass
# 含有yield指令的函數可以稱為生成器
def g():
    yield()
print(type(f()),isinstance(f(),Iterable))
print(type(g()),isinstance(g(),Iterable))

import os
# 生成器是迭代器的一種，讓函數對象內部進行迭代
# 可以實現讓函數內部暫停，實現瞭程序的異步功能，同時也實現瞭解耦。

def my_input():
    global str    
    str = input('input a line')
    pass

def my_write():
    with open('workfile.txt','w') as f:
        while(str):
            f.write(str+'\n')
            yield()
        return 


mw = my_write()
while(True):
    my_input()
    try:
        next(mw)
    except StopIteration:
        pass
    if not str:
        break   

# 不帶參數的裝飾器
from functools import wraps
# 裝飾器封裝一個函數，並且用這樣或者那樣的方式來修改它的行為。
def mydecorator(a_func):
    @wraps(a_func)  #聲明這個註解就可以不重寫傳入的函數，隻是調用的時候wrap一下。不加的話，a_func函數可以看作被重寫為wrapTheFunction.
    def wrapTheFunction():
        print(f"function in {id(a_func)} starts...")
        a_func()
        print(f"function in {id(a_func)} ends...")
    return wrapTheFunction

# 在函數定義前加入此註解就可以將函數傳入裝飾器並包裝
@mydecorator
def f():
    print('hi')
    pass

f()
print(f.__name__)

# 帶參數的裝飾器(實現輸出到自定義的日志文件)
from functools import wraps

def logit(logfile='out.log'):
    def mydecorator2(a_func):
        @wraps(a_func)
        def wrapTheFunction(*args, **kwargs):   # 這個保證瞭函數可以含有任意形參
            log_string = a_func.__name__ + " was called"
            print(log_string)
            # 打開logfile，並寫入內容
            with open(logfile, 'a') as opened_file:
                # 現在將日志打到指定的logfile
                opened_file.write(log_string + '\n')
                return a_func(*args, **kwargs)
        return wrapTheFunction
    return mydecorator2

# func group1 
@ logit('out1.log')
def func1(str):
    print(str)
    pass
@ logit('out2.log')
def func2(): pass
            
func1('I have a foul smell')
func2()        

# 帶參數的裝飾器(實現輸出到自定義的日志文件)
from functools import wraps

def logit(logfile='out.log'):
    def mydecorator2(a_func):
        @wraps(a_func)
        def wrapTheFunction(*args, **kwargs):   # 這個保證瞭函數可以含有任意形參
            log_string = a_func.__name__ + " was called"
            print(log_string)
            # 打開logfile，並寫入內容
            with open(logfile, 'a') as opened_file:
                # 現在將日志打到指定的logfile
                opened_file.write(log_string + '\n')
                return a_func(*args, **kwargs)
        return wrapTheFunction
    return mydecorator2

# func group1 
@ logit('out1.log')
def func1(str):
    print(str)
    pass
@ logit('out2.log')
def func2(): pass
            
func1('I have a foul smell')
func2()