Python晋级语法

Python晋级语法

1.上下文管理器

with open("1.csv","r") as f:
    for i in f:
        print(i)

class DemoClass(object):
    def __init__(self,name):
        self.name=name
    def __enter__(self):#重载__enter__()方法
        print("进入上下文管理器")
        return self
    def __exit__(self, exc_type, exc_val, exc_tb):#重载__exit__()方法
        print("退出上下文管理器")
    def run(self):
        print("DemoClass的某个实例对象在运行")
with DemoClass("Python123") as f:#as引用的是__enter__的返回值
    f.run()

2.迭代器

class Demolterator(object):
    def __init__(self,container):
        self.container=container
        self.salt=len(self.container)
    def __iter__(self):
        return self
    def __next__(self):
        self.salt-=1
        print(self.salt)
        if self.salt>=0:
            return self.container[self.salt]
        else:
            raise StopIteration
di=Demolterator([1,2,3,4,5,6,7,8])
for i in di:
    print(i,end="")

import time
class Demolterator(object):
    def __init__(self,container):
        self.container=container
    def __iter__(self):
        return self
    def __next__(self):
        self.container=self.container+1
        return self.container

di=Demolterator(1)
for i in di:
    print(i)
    time.sleep(1)

3.生成器

#设计原则
#1.函数中有迭代/循环过程
#2.每次结果以yield方式表达
#3.结合for..in..使用
def getValue(max):
    import random
    ls=list(range(10))
    print(ls,end="")
    for i in range(max):
        yield ls[random.randint(0,9)]
for i in getValue(10):
    print(i)

4.装饰器

"""将函数作为参数传给另一个函数
装饰器函数必须返回一个函数对象引用，否则无法利用语法糖，因此需要内部定义一个函数
fi(age)(f2(func))

@fi(arg)
@f2
def func():
    pass
"""
def bar(foo):
    def wrapper(a):
        print("{:*^20}".format("BEGIN"))
        foo(a)
        print("{:*^20}".format("END"))
    return wrapper

@bar
def printA(a):
    print(f"这是变量{a}")
printA("Python123")

from datetime import datetime
import time
def bar(foo):
    def wrapper():
        print("开始时间",datetime.now())
        foo()
        print("结束时间",datetime.now())
    return wrapper
@bar
def printA():
    print("程序开始运行")
    time.sleep(3)
    print("程序结束运行")
printA()