Python学习之——装饰器

Python学习之——装饰器

参考

python装饰器的4种类型：函数装饰函数、函数装饰类、类装饰函数、类装饰类

9.4 定义一个带参数的装饰器

Python – 在装饰器中获取原始函数参数

基础

闭包概念

Python闭包（Closure）详解

闭包概念：在一个内部函数中，对外部作用域的变量进行引用，并且外部函数的返回值为内部函数，那么内部函数就叫做闭包。

示例：

def outer_func(year):
    def inner_func(month):
        print(f'year:{year}, month:{month}')
    return inner_func

closure_func = outer_func('2023')
closure_func (12)

调用func时，产生了闭包inner_func，其持有外层函数的自由变量year，当函数func的生命周期结束之后，year这个变量依然存在，因为它被闭包引用了，不会被回收。

闭包的特点:
内部函数可以读取外层函数内的局部变量，并让其常驻内存，不会被回收，所以注意内存泄漏

装饰器

一文搞懂什么是Python装饰器

装饰器是用来增强函数/类功能的一个函数

import logging


def no_arg_decorator(func):
    call_count = 0

    def inner_func(*arg, **kwargs):
        # do somethings, example
        nonlocal call_count
        call_count += 1
        print(f'call {func.__name__} func, total call count:{call_count }')
        func(*arg, **kwargs)
    return inner_func


def arg_decorator(*outer_arg, **outer_kwargs):
    def inner_func(func):
        def inner_func2(*arg, **kwargs):
            # do somethings use outer_arg, outer_kwargs, example
            file_path = outer_kwargs.get('log_file_path')
            if file_path:
                logging.basicConfig(filename=file_path,
                                    format='%(asctime)s - %(name)s - %(levelname)s - %(message)s-%(funcName)s',
                                    level=logging.DEBUG)
                logging.debug(f'debug, call {func.__name__}, arg:{arg}, kwargs:{kwargs}')
            func(*arg, **kwargs)
        return inner_func2
    return inner_func


def test_func1(a=1):
    pass


# 1.不用语法糖@符号​​​​​​​
# 1.1 无参装饰器
wraped_func1 = no_arg_decorator(test_func1)

# 1.2 有参装饰器
wraped_func2 = arg_decorator(log_file_path='log.txt')(test_func1)


# 2.采用语法糖@符号​​​​​​​
# 2.1 无参装饰器
@no_arg_decorator
def test_func2(a=1):
    pass


# 2.2 有参装饰器
@arg_decorator(log_file_path='log.txt')
def test_func3(a=1):
    pass


if __name__ == '__main__':
    print('=========================')
    wraped_func1()
    wraped_func1()
    wraped_func2(a=11)

    test_func2()
    test_func3(a=111)


# 结果
=========================
call test_func1 func, total call count:1
call test_func1 func, total call count:2
call test_func2 func, total call count:1

系统自带的装饰器

@property

Python 中 property() 函数及 @property 装饰器

class Food(object):
	def __init__(self):
		self._price = 0

    @property
    def price(self):
        return self._price 

    @price.setter
    def price(self, value):
        if value < 0:
            raise ValueError('price must large than 0!')
        self._price = value
    
    @price.deleter
    def price(self):
    	del self._price 
 

@staticmethod

staticmethod修饰过的方法叫静态方法，可以直接通过类调用方法，这样做的好处是执行效率比较高，也可以通过实例调用该方法。

from datetime import datetime

TIME_FORMAT_STR = "%Y/%m/%d/ %H:%M:%S"

class TimeUtil():

    @staticmethod
    def timestamp_to_utc_str(timestamp: float, format_str=TIME_FORMAT_STR) -> str:
	    """时间戳转utc-0时区的时间"""
	    datetime_obj: datetime = datetime.utcfromtimestamp(timestamp)
	    return datetime_obj.strftime(format_str)

	@staticmethod
	def timestamp_to_local_str(timestamp: float, format_str=TIME_FORMAT_STR) -> str:
	    """时间戳转当前本地时区的时间"""
	    datetime_obj: datetime = datetime.fromtimestamp(timestamp)
	    return datetime_obj.strftime(format_str)

@classmethod

classmethod修饰过的方法叫类方法，可以直接通过类或者实例调用方法

利用@classmethod实现单例模式

from datetime import datetime


class SingletonBase(object):
    __instance = None

    @classmethod
    def get_instance(cls, *arg, **kwargs):
        if cls.__instance is None:
            cls.__instance = cls()
            cls.__instance.init(*arg, **kwargs)
        return cls.__instance

    def init(self, *arg, **kwargs):
        pass


class TestMgr(SingletonBase):

    def init(self, *arg, **kwargs):
        print(f'I am TestMgr Singleton, arg:{arg}, kwargs:{kwargs}')


if __name__ == '__main__':
	test_mgr = TestMgr.get_instance('hello', 'world', time=datetime.now().strftime("%Y/%m/%d/ %H:%M:%S"))

自定义装饰器

python装饰器2：类装饰器
python装饰器的4种类型：函数装饰函数、函数装饰类、类装饰函数、类装饰类

函数的装饰器

无参数

import time

all_func = {}

# 用于函数注册的装饰器
def register_func(func):
    all_func[func.__name__] = func
    return func


# 用于统计函数耗时的装饰器
def calc_time(func):
    def inner_func():
        start = time.time()
        func()
        end = time.time()
        print(
            f'call {func.__name__} func, cost time:{int(end - start)} second')
    return inner_func


@calc_time
def test_func4():
    time.sleep(2)


if __name__ == '__main__':
    print('=========================')
    test_func4()

# 结果
=========================
call test_func4 func, cost time:2 second

有参数

# -*- coding:utf-8 -*-
from functools import wraps


test_dict = {}


def Decorator(arg1=0, arg2=1):
    def inner_func(func):
        funcName = func.__name__
        test_dict[funcName] = func
        # 没有return func，则该装饰器默认返回None，会导致被Decorator装饰后的函数无法被调用，
        # 有return func，则被Decorator装饰后的函数还是被赋值为原函数，后续还可以调用
        # return func
    return inner_func


def decorator(*arg):
    return Decorator(*arg)


def Decorator2(arg1=0, arg2=1):
    def inner_func(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            # do something
            return func(*args, **kwargs)

        funcName = func.__name__
        test_dict[funcName] = func
        # 有return wrapper，则被Decorator2装饰后的函数还是被赋值为原函数，后续还可以调用
        return wrapper
    return inner_func


def decorator2(*arg):
    return Decorator2(*arg)


@Decorator()
def test_func_a():
    pass


@decorator()
def test_func_b():
    pass


@Decorator2()
def test_func_c():
    pass


@decorator2()
def test_func_d():
    pass

if __name__ == "__main__":
    print(test_dict)

# 结果
{'test_func_a': <function test_func_a at 0x000001F7B6851D00>, 'test_func_b': <function test_func_b at 0x000001F7B6851DA0>, 'test_func_c': <function test_func_c at 0x000001F7B6851E40>, 'test_func_d': <function test_func_d at 0x000001F7B6851F80>}

类的装饰器

无参数

# decorator1(cls)返回一个函数inner_func的写法
def decorator1(cls):
    def inner_func(a):
        print('class name:', cls.__name__)
        return cls(a)
    return inner_func


# decorator2(cls)返回一个类inner_cls的写法
def decorator2(cls):
    class inner_cls:
        def __init__(self, *args, **kwargs):
            self.wrapped_obj = cls(*args, **kwargs)

        def __getattr__(self, name):
            return getattr(self.wrapped_obj, name)
    return inner_cls


@decorator1
class FooClass1():
    def __init__(self, a):
        self.a = a

    def fun(self):
        print('self.a =', self.a)

@decorator2
class FooClass2():
    def __init__(self, a):
        self.a = a

    def fun(self):
        print('self.a =', self.a)

foo1 = FooClass1('Foo1_a')
foo1.fun()

foo2 = FooClass2('Foo2_a')
foo2.fun()

有参数

1.通过装饰器实现子类的自动注册

all_subcls = {}

def register_subcls(base_cls_name):
    def decorate(sub_cls):
        if base_cls_name not in all_subcls :
            all_subcls[base_cls_name] = {}
       all_subcls[base_cls_name][sub_cls.__name__] = sub_cls
    return decorate

def get_subcls(base_cls_name, sub_cls_name):
	if base_cls_name not in all_subcls:
		return None
	else:
		return all_subcls[base_cls_name].get(sub_cls_name)

# 使用
class TestBase1(object):
	@staticmethod
	def create_instance(sub_cls_name, *args, **kwargs):
		sub_cls = get_subcls('TestBase1', sub_cls_name)
		return sub_cls(*args, **kwargs) if sub_cls else None
	
	def __init__(self, *args, **kwargs):
		self.args = args
		self.kwargs = kwargs
	
	def print_self(self):
		print(f'TestBase1, args:{args}, kwargs:{kwargs}')


@register_subcls('TestBase1')
class TestA(TestBase1):
	def print_self(self):
		print(f'TestA, args:{args}, kwargs:{kwargs}')

@register_subcls('TestBase1')
class TestB(TestBase1):
	def print_self(self):
		print(f'TestB, args:{args}, kwargs:{kwargs}')

2. 通过装饰器给类增加静态函数/类函数/成员函数

# 实例方法
def add_instance_method(cls):
    def inner_func(func):
        setattr(cls, func.__name__, func)
    return inner_func


# 类方法
def add_class_method(cls):
    def inner_func(func):
        setattr(cls, func.__name__, classmethod(func))
    return inner_func


# 静态方法
def add_static_method(cls):
    def inner_func(func):
        setattr(cls, func.__name__, staticmethod(func))
    return inner_func


def add_func_decorator(cls):

    @add_instance_method(cls)
    def test_instance_func(self):
        print('test_instance_func')

    @add_class_method(cls)
    def test_class_func(cls):
        print('test_class_func')

    @add_static_method(cls)
    def test_static_func():
        print('test_static_func')

    return cls


@add_func_decorator
class TestClass():
    def __init__(self):
        pass


if __name__ == '__main__':
    TestClass.test_class_func()
    TestClass.test_static_func()
    test_obj = TestClass()
    test_obj.test_instance_func()

# 结果
test_class_func
test_static_func
test_instance_func

@functools.wraps

functools.wraps对我们的装饰器函数进行了装饰之后，消除了装饰器对原函数的影响。
具体Python装饰器深度解析

装饰器类

之前都是用函数来构造装饰器，其实类也可以用来构建装饰器
装饰器类

先熟悉一下Python __call__()方法
Python 中，凡是可以将 () 直接应用到自身并执行，都称为可调用对象。可调用对象包括自定义的函数、Python 内置函数以及本节所讲的类实例对象。
__ call__()方法的功能类似于在类中重载 () 运算符，使得类实例对象可以像调用普通函数那样，以“对象名()”的形式使用。

from functools import wraps

class logit(object):
    def __init__(self, logfile='out.log'):
        self.logfile = logfile

    def __call__(self, func):
        @wraps(func)
        def wrapped_function(*args, **kwargs):
            log_string = func.__name__ + " was called"
            print(log_string)
            with open(self.logfile, 'a') as fp:
                fp.write(log_string + '\n')
            # 发送一个通知
            self.notify()
            return func(*args, **kwargs)
        return wrapped_function

    def notify(self):
        pass
 
# 使用
@logit()
def myfunc1():
    pass

装饰器实现单例模式

Python单例模式(Singleton)的N种实现

1.使用函数装饰器实现单例

def Singleton(cls):
    _instance = {}

    def inner():
        if cls not in _instance:
            _instance[cls] = cls()
        return _instance[cls]
    return inner
    
@Singleton
class Cls(object):
    def __init__(self):
        pass

cls1 = Cls()
cls2 = Cls()
print(id(cls1) == id(cls2))

2.使用类装饰器实现单例

class Singleton(object):
    def __init__(self, cls):
        self._cls = cls
        self._instance = {}

    def __call__(self):
        if self._cls not in self._instance:
            self._instance[self._cls] = self._cls()
        return self._instance[self._cls]

@Singleton
class Cls2(object):
    def __init__(self):
        pass

cls1 = Cls2()
cls2 = Cls2()
print(id(cls1) == id(cls2))

# 同时，由于是面对对象的，这里还可以这么用
class Cls3():
    pass

Cls3 = Singleton(Cls3)
cls3 = Cls3()
cls4 = Cls3()
print(id(cls3) == id(cls4))

作者：selfsongs