[Day1]PythonAdvanced学习笔记-装饰器decorator

[PythonAdvanced] 学习笔记 - Day 1

概览

Date: 2024-11-26 Time Spent: 6 hours

Topics: Decorators Difficulty: ⭐⭐⭐☆☆ (1-5 stars)

学习内容

1. [*args & **kwargs]

   • 概念: (使用中*是必须的，名称可以根据个人习惯更换)

     *args is used to send a non-keyworded variable length argument list to the function. *args用来传递没有keyword的值。

     **kwargs allows you to pass keyworded variable length of arguments to a function. **kwargs是用来传递有keyword的值。

   • *args Example code

     def test_var_args(f_arg, *argv):
      print("first normal arg:", f_arg)
      for arg in argv:
      print("another arg through *argv:", arg)
     
     >>> test_var_args('yasoob', 'python', 'eggs', 'test')
     first normal arg: yasoob
     another arg through *argv: python
     another arg through *argv: eggs
     another arg through *argv: test
     

   • **kwargs Example code

     def greet_me(**kwargs):
         for key, value in kwargs.items():#遍历字符串
             print("{0} = {1}".format(key, value))#以key=value的格式化形式输出
     
     >>> greet_me(name="yasoob") //key=name, value=yasoob
     name = yasoob
     

2. [Decorators]

   • 概念: 不改变原代码的基础上，对函数进行修饰。

   • Example code

     def decorator(func):
      def wrapper():
          print("Something is happening before the function is called.")
          func()
          print("Something is happening after the function is called.")
      return wrapper 
     def say_whee():
      print("Whee!") 
     say_whee = decorator(say_whee)
     

   • Example code

     def do_twice(func):
         def wrapper_do_twice(*args, **kwargs):
             func(*args, **kwargs)
             func(*args, **kwargs)
         return wrapper_do_twice
     
     @do_twice # greet = do_twice(greet)
     def greet(name):
         print(f"Hello {name}")
     >>> greet(name = "Mia")
     

   • Example code

     def do_twice(func):
         def wrapper_do_twice(*args, **kwargs):
             func(*args, **kwargs)
             func(*args, **kwargs)
             return func(*args, **kwargs)
         return wrapper_do_twice
     
     @do_twice
     def return_greeting(name):
         print("Creating greeting")
         return f"Hi {name}"
     
     >>> return_greeting("Adam")
     Creating greeting
     Creating greeting
     'Hi Adam'
     

   • Example code

     import functools
     def do_twice(func):
         @functools.wraps(func) 
         def wrapper_do_twice(*args, **kwargs):
             func(*args, **kwargs)
             return func(*args, **kwargs)
         return wrapper_do_twice
     @do_twice
     def say_whee():
         print("Whee!")
     
     >>> say_whee
     <function say_whee at 0x7ff79a60f2f0>
     
     >>> say_whee.__name__
     'say_whee'
     
     >>> help(say_whee)
     Help on function say_whee in module whee:
     

   • Example code

     import functools
     
     def decorator(func):
         @functools.wraps(func)
         def wrapper_decorator(*args, **kwargs):
             # Do something before
             value = func(*args, **kwargs)
             # Do something after
             return value
         return wrapper_decorator
     

   • Timer Example Code

     import functools
     import time
     
     def timer(func):
         """Print the runtime of the decorated function"""
         @functools.wraps(func)
         def wrapper_timer(*args, **kwargs):
             start_time = time.perf_counter()
             value = func(*args, **kwargs)
             end_time = time.perf_counter()
             run_time = end_time - start_time
             print(f"Finished {func.__name__}() in {run_time:.4f} secs")
             return value
         return wrapper_timer
     
     @timer
     def waste_some_time(num_times):
         for _ in range(num_times):
              sum([number**2 for number in range(10_000)])
     
     >>> waste_some_time(1)
     Finished waste_some_time() in 0.0010 secs
     
     >>> waste_some_time(999)
     Finished waste_some_time() in 0.3260 secs
     

练习代码

# *args and **kwargs 传递不定数量的值，如没有规定数量的字符串等
# 当使用 * 解包时，如果传入的是一个字符串，它会将字符串解包为字符序列。
# 当使用 ** 解包时，如果传入的是一个字典，它会将字典解包为关键字参数。

def test_args(value, *args):
    print("first:", value)
    for arg in args:
        print("next:", arg)


# test_args('hello','world','three','four')

def test_kwargs(**kwargs):
    for key, value in kwargs.items():
        print("{} = {}".format(key, value))


# test_kwargs(name='GPT',age='0.5 year',sex='none')

def test_args_and_kwargs(name, age, sex):
    print("name:", name)
    print("age:", age)
    print("sex:", sex)


args = ("GPT", "0.5 year", 'none')
# test_args_and_kwargs(*args)
kwargs = {"name": 'GPT', "sex": 'none', "age": '0.5 year'}


# test_args_and_kwargs(**kwargs) #使用**输出时需要注意列表里的key要与函数里的key对应

def decorator(func):
    def wrapper():  # 包装内容
        print("before the function")
        func()
        print("after the function")

    return wrapper


def say_hello():
    print("hello!")


# say_hello() #装饰前
say_hello = decorator(say_hello)  # 装饰后的


# say_hello()

@decorator  # 文法糖的装饰功能与say_hello = decorator(say_hello)功能一致
def say_hi():
    print("hi")


# say_hi()

import functools

def do_twice(func):
    @functools.wraps(func)  # 使用 @ functools.wraps裝飾器，它將保留有關原始函數的資訊
    def wrapper(*args, **kwargs):  # 接受任意數量的參數並將它們傳遞給它修飾的函數
        func(*args, **kwargs)
        func(*args, **kwargs)
        return func(*args, **kwargs)  # 保证如果与需求，可以回传函数值

    return wrapper


@do_twice
def say_hello(name):
    print("hello!", name)


# say_hello('Arden')
info = "Arden"
# say_hello(*info) #无法实现，*会将“Arden”解包为字符序列，因此有五个参数，与函数不符。
# say_hello(info)
info_me = {"name": "Arden"}
# say_hello(**info_me)

import functools  # 装饰器模板
import time

def timer(func):
    # 用来统计函数运行时间
    @functools.wraps(func)
    def wrapper_decorator(*args, **kwargs):
        start_time = time.time()  # 统计开始时时间
        value = func(*args, **kwargs)
        end_time = time.time()  # 记结束时间
        time_taken = end_time - start_time #时间差值
        print("It takes", time_taken, "seconds")
        return value
    return wrapper_decorator

@timer
def waste(num):
    for i in range(num):
        sum([i**2 for i in range(10000)]) #计算(1+...+2i)的和(i<=10000)

#waste(1)
#waste(999)

遇见的挑战难及解决方法和笔记点见注释。

学习资源

• [Python Tips]: A book of many contents like generators, decorators, mutation and so on.
• [Real Python]: Primer on Python Decorators.

明日计划

• 上下文管理器（with语句）

• 面向对象进阶（元类、属性描述符）

• 迭代器和生成器