Python retains metadata methods for decorated functions

This article mainly introduces in detail how python retains metadata for decorated functions. I hope it can help you.

Case:

The function object stores some function metadata, such as:

f.__name__ Function name

                                                                                                                                                                                                               f.__defaults__                                                                                                                                                      

After using the decorator, when accessing the above properties in the decorator, what we see is the metadata of the decorator function

Implemented in the decorator function, retaining the metadata of the decorated function

                                                                                                                                                                implemented through the wraps and update_wrapper methods in functools, each of which can be implemented independently

#!/usr/bin/python3
 
import time
from functools import (wraps, update_wrapper, WRAPPER_ASSIGNMENTS, WRAPPER_UPDATES)
 
 
def count_time(func):
  """
  给目标函数加上计算运行时间统计
  """
  # 这个装上器和update_wrapper一样，默认参数WRAPPER_ASSIGNMENTS, WRAPPER_UPDATES
  @wraps(func)
  def wrapper(*args, **kwargs):
    start_time = time.time()
     
    # 定义result接收函数返回值，并且在装饰函数最后返回回去
    resutl = func(*args, **kwargs)
    print('运行时间：', time.time()-start_time)
    return resutl
   
  # 其中默认参数 WRAPPER_ASSIGNMENTS, WRAPPER_UPDATES
  # update_wrapper(wrapper, func)
  return wrapper
 
 
@count_time
def add(num=100):
  """
  计算 0~num 累加值，默认num=100
  """
  time.sleep(1)
  return sum([x for x in range(num+1)])
 
if __name__ == '__main__':
  print('函数名：', add.__name__)
  print('属性字典：', add.__dict__)
  print('函数默认参数：', add.__defaults__)
  print('函数所在模块：', add.__module__)
  print('函数文档：', add.__doc__)
   
  # 打印两个默认参数
  print(WRAPPER_ASSIGNMENTS, WRAPPER_UPDATES)
  result = add()
  print(result)

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