python中的decorator模块

Posted 2020-08-16

decorator模块是python用来专门封装装饰器的模块，使用decorator构造装饰器更加简便，同时被装饰的函数签名也保留不变

from decorator import decorator


@decorator
def check_num(func, *args, **kwargs):
    if len(args) != 2:
        raise Exception(‘Your args number is not two‘)
    else:
        return func(*args, **kwargs)


@check_num
def add(x, y):
    return x + y

　　

>>> add
<function add at 0x0000000002D43BA8>
>>> print add(1,2)
3
...
>>> add(1,2,3)
Traceback (most recent call last):
  File "D:\PyCharm 5.0.4\helpers\pydev\pydevd_exec.py", line 3, in Exec
    exec exp in global_vars, local_vars
  File "<input>", line 1, in <module>
TypeError: add() takes exactly 2 arguments (3 given)

#可以看到这里当我们传三个参数给add()函数时，他直接从add()函数抛出类型错误异常，
#并没有进入check_num装饰器进行参数校验，可见被装饰的函数add()的签名还是他本身
#如果直接构造装饰器，那么这里将会从check_num里面抛出异常，如下：

def check_num(func):
    def inner(*args,**kwargs):
        if len(args) != 2:
            raise Exception(‘Your args number is not two‘)
        else:
            return func(*args,**kwargs)
    return inner

@check_num
def add(x, y):
    return x + y


>>> add
<function inner at 0x0000000002E233C8>
>>>add(1,2,3)
Traceback (most recent call last):
  File "D:\PyCharm 5.0.4\helpers\pydev\pydevd.py", line 2411, in <module>
    globals = debugger.run(setup[‘file‘], None, None, is_module)
  File "D:\PyCharm 5.0.4\helpers\pydev\pydevd.py", line 1802, in run
    launch(file, globals, locals)  # execute the script
  File "E:/code/my_project/decorator/test3.py", line 14, in <module>
    print add(1,2,3)
  File "E:/code/my_project/decorator/test3.py", line 4, in inner
    raise Exception(‘Your args number is not two‘)
Exception: Your args number is not two

如果想让装饰器带参数呢？

from decorator import decorator


def check(flag):
    @decorator
    def check_num(func, *args, **kwargs):
        if flag == ‘false‘:
            print ‘skip check !‘
            return func(*args,**kwargs)
        if len(args) != 2:
            raise Exception(‘Your args number is not two‘)
        else:
            return func(*args, **kwargs)
    return check_num


@check(‘false‘)
def add(x, y):
    return x + y

>>>add
<function add at 0x0000000002C53C18>
>>>add(1,2)
skip check !
3