[Python知识库]python代码：高级闭包和装饰器的例子

python代码：高级闭包和装饰器的例子

#!/usr/bin/python
# -*- coding: UTF-8 -*-
"""
@author:
@file:funcLog.py
@time:2022-04-03 20:37
"""
# 书《Python核心编程(第二版).pdf》，作者：Wesley J. Chun
# 例子：高级闭包和装饰器的例子
# 应用程序logs函数调用。
# 用户选择是要在函数调用之前或者之后，把函数调用写入日志。如果选择贴日志，执行时间也会显示出来。
# 这个例子演示了带参数的装饰器，该参数最终决定哪一个闭包会被调用的。这也是闭包的威力的特征。

# from time import time
import time

def logged(when):
    print("The value of when: ", when)
    def log(f, *args, **kargs):
        print('''Called:
    function: %s
    args: %r
    kargs: %r''' % (f, args, kargs))
        time.sleep(1)  # 因为电脑运行的速度太快了，统计程序运行的时间总是0，所以人为延迟1秒，从而使运行时间不为0.

    def pre_logged(f):
        def wrapper(*args, **kargs):
            log(f, *args, **kargs)
            return f(*args, **kargs)
        return wrapper

    def post_logged(f):
        def wrapper(*args, **kargs):
            # now = time()
            now = time.time()
            try:
                return f(*args, **kargs)
            finally:
                log(f, *args, **kargs)
                # print("time delta: %s" % (time() - now))
                print("time delta: %s" % (time.time() - now))
        return wrapper

    try:
        # # 解释：{...}里的东东为字典，[...]里的东东为字典的键key。连在一起看，就是返回字典中指定key对应的value。
        # # 所以那一行return {...}[...]代码等价于以下几行代码：
        # dict_return = {"pre": pre_logged, "post": post_logged}
        # key_return = when
        # return dict_return[key_return]
        return {"pre": pre_logged,
                "post": post_logged}[when]
    except KeyError as e:
        # print(type(e))  # <class 'KeyError'>
        # print(e)  # 'wrong'
        # print(repr(e))  # KeyError('wrong')
        raise ValueError(repr(e), 'must be "pre" or "post"')  # ValueError: (KeyError('wrong'), 'must be "pre" or "post"')

# @logged("pre")  # 装饰器  # 等同于： hello = logged("pre")(hello("world!"))
@logged("post")  # 装饰器  # 等同于： hello = logged("post")(hello("world!"))
# @logged("wrong")  # 装饰器  # 等同于： hello = logged("wrong")(hello("world!"))
def hello(name):
    print("Hello,", name)

if __name__ == "__main__":
    hello("World!")

"""
当装饰器是@logged("pre")时，输出结果如下：
The value of when:  pre
Called:
    function: <function hello at 0x000001E82EF36550>
    args: ('World!',)
    kargs: {}
Hello, World!
----
当装饰器是@logged("post")时，输出结果如下：
The value of when:  post
Hello, World!
Called:
    function: <function hello at 0x0000022DDF5CB9D0>
    args: ('World!',)
    kargs: {}
time delta: 1.002335786819458
----
当装饰器是@logged("wrong")时，输出结果如下：
Traceback (most recent call last):
  File "E:\workspace\PycharmProjects\project01\com\study\pythoncore\ch02\funcLog.py", line 50, in logged
    return {"pre": pre_logged,
KeyError: 'wrong'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "E:\workspace\PycharmProjects\project01\com\study\pythoncore\ch02\funcLog.py", line 58, in <module>
    @logged("wrong")  # 装饰器  # 等同于： hello = logged("wrong")(hello("world!"))
  File "E:\workspace\PycharmProjects\project01\com\study\pythoncore\ch02\funcLog.py", line 56, in logged
    raise ValueError(repr(e), 'must be "pre" or "post"')  # ValueError: (KeyError('wrong'), 'must be "pre" or "post"')
ValueError: ("KeyError('wrong')", 'must be "pre" or "post"')
The value of when:  wrong

Process finished with exit code 1

"""