python3-cookbook笔记：第九章 元编程

import time
from functools  wraps


def timethis(func):
    """普通的装饰器"""

    def wrapper(*args,**kwargs):
        start = time.time()
        result = func(*args,1)">kwargs)
        end = time.time()
        print(func.__name__,end - start)
        return result

     wrapper


 timethis_wraps(func):
    有wraps的装饰器"""

    @wraps(func)
     wrapper


@timethis
 countdown(n):
    timethis装饰函数"""
    while n > 0:
        n -= 1


@timethis_wraps
 countdown_wraps(n):
    timethis_wraps装饰函数


countdown(1000)
print(countdown.__name____doc__)

countdown_wraps(1000print(countdown_wraps.__doc__)

countdown 0.0
wrapper
None
countdown_wraps 0.0
countdown_wraps
timethis_wraps装饰函数

 logging
 wraps,partial


# 星号*的作用是迫使其后面的参数，即level，name，message三个参数，都必须使用关键字参数的形式传参
def logged(func=None,*,level=logging.DEBUG,name=None,message=None):
    if func is None:
         此处partial的作用为返回一个函数，但它的level，name，message三个参数是已经指定好了的
         使用的时候只需要传入剩下的参数即可，相当于：def logged(func=None):...
        return partial(logged,level=level,name=name,1)">message)

    logname = name if name else func.__module__
    log = logging.getLogger(logname)
    logmsg = message if message __name__

     使用wraps装饰器保证func函数的元信息是正确完整的
    @wraps(func)
    kwargs):
        log.log(level,logmsg)
        return func(*args,1)">kwargs)

     不传参示例
@logged
 add(x,y):
    return x + y


 传参示例
@logged(level=logging.CRITICAL,name='example' spam():
    print(Spam!)


print(add(2,3))   输出：5
spam()   输出：Spam!

class A:
     实例方法
     decorator1(self,func):
         wrapper函数不用定义参数self
        @wraps(func)
        kwargs):
            Decorator 1)
            kwargs)

         wrapper

     类方法
    @classmethod
     decorator2(cls,1)"> wrapper函数不用定义参数cls
Decorator 2 wrapper


a = A()


 使用实例进行调用
@a.decorator1
pass


 使用类进行调用
@A.decorator2
 grok():
    pass

 Person:
    def __init__(self,name,age):
        self.name = name
        self.age = age

    @property
     name(self):
         self._name

    @name.setter
     name(self,value):
        if not isinstance(value,str):
            raise TypeError(name must be a string)
        self._name = value

    @property
     age(self):
         self._age

    @age.setter
     age(self,int):
            age must be an int)
        self._age = value

 此函数返回一个属性对象，用于检查赋的值是否为指定的类型
# 在类中使用这个函数时，跟把这个函数中的代码放到类中定义是一样的，作用就只是把重复使用的代码提出来了
 typed_property(name,expected_type):
    storage_name = _' + name

    @property
     prop(self):
         getattr(self,storage_name)

    @prop.setter
     prop(self,expected_type):
            {} must be a {}.format(name,expected_type))
        setattr(self,storage_name,value)

     prop


 Person:
    name = typed_property(name,str)
    age = typed_property(age name
        self.age = age

 partial

String = partial(typed_property,expected_type=str)
Integer = partial(typed_property,1)">int)


 Person:
    name = String()
    age = Integer()

     name
        self.age = age

from contextlib  contextmanager


@contextmanager
 list_transaction(orig_list):
    working = list(orig_list)
    yield working
     如果没有报错，对列表orig_list的任何修改才会生效
    orig_list[:] = working


items = [1,2,3]
with list_transaction(items) as working:
    working.append(4)
    working.append(5print(items)

items = [1,1)">)
    raise RuntimeError(oops！print(items)

[1,3,4,5]
Traceback (most recent call last):
  File "Z:/Projects/Daily Test/test.py",line 120,in <module>
    raise RuntimeError('oops！')
RuntimeError: oops！

>>> a = 13
>>> exec(b = a + 1)
>>> b
14

>>>  test():
    a = 13
    (b)

    
>>>  b并没有在真实局部变量域中，所以会报错
>>> test()
Traceback (most recent call last):
  File "<pyshell#3>",line 1,in <module>
    test()
  File <pyshell#1>in test
    (b)
NameError: name b' is  defined
>>> 

>>>  test1():
    x = 0
    x += 1(x)

    
>>> test1()   x的值并没有被修改
0
>>> 

>>>  test2():
    x = 0
    loc = locals()
    before:after:x = 想要获取修改后的值，可以从locals()中获取
    x = loc[x]
     注意，再次运行locals()时，原来的值会被覆盖掉
    x = 444
    loc =new: test2()
before: {: 0}
after: {': 1,loc: {...}}
x = 0
x = 1
new: {': 444,1)">: {...}}
>>>