www.cnblogs.com/alex3714/category/770733.html
静态方法
只是名义上归类管理, 实际上在静态方法里访问不了类或实例中的任何属性
通过@staticmethod装饰器即可把其装饰的方法变为一个静态方法,什么是静态方法呢?其实不难理解,普通的方法,可以在实例化后直接调用,并且在方法里可以通过self.调用实例变量或类变量,但静态方法是不可以访问实例变量或类变量的,一个不能访问实例变量和类变量的方法,其实相当于跟类本身已经没什么关系了,它与类唯一的关联就是需要通过类名来调用这个方法
class
Dog(
object
):
def
__init__(
self
,name):
self
.name
=
name
@staticmethod
#把eat方法变为静态方法
def
eat(
self
):
print
(
"%s is eating"
%
self
.name)
d
=
Dog(
"ChenRonghua"
)
d.eat()
上面的调用会出以下错误,说是eat需要一个self参数,但调用时却没有传递,没错,当eat变成静态方法后,再通过实例调用时就不会自动把实例本身当作一个参数传给self了。
Traceback (most recent call last):
File
"/Users/jieli/PycharmProjects/python基础/自动化day7面向对象高级/静态方法.py"
, line
17
,
in
<module>
d.eat()
TypeError: eat() missing
1
required positional argument:
'self'
想让上面的代码可以正常工作有两种办法
1. 调用时主动传递实例本身给eat方法,即d.eat(d)
2. 在eat方法中去掉self参数,但这也意味着,在eat中不能通过self.调用实例中的其它变量了
class Dog(object):
def __init__(self,name):
self.name = name
@staticmethod
def eat():
print(" is eating")
d = Dog("ChenRonghua")
d.eat()
类方法
只能访问类变量,不能访问实例变量
类方法通过@classmethod装饰器实现,类方法和普通方法的区别是, 类方法只能访问类变量,不能访问实例变量
class
Dog(
object
):
def
__init__(
self
,name):
self
.name
=
name
@classmethod
def
eat(
self
):
print
(
"%s is eating"
%
self
.name)
d
=
Dog(
"ChenRonghua"
)
d.eat()
Traceback (most recent call last):
File
"/Users/jieli/PycharmProjects/python基础/自动化day7面向对象高级/类方法.py"
, line
16
,
in
<module>
d.eat()
File
"/Users/jieli/PycharmProjects/python基础/自动化day7面向对象高级/类方法.py"
, line
11
,
in
eat
print
(
"%s is eating"
%
self
.name)
AttributeError:
type
object
'Dog'
has no attribute
'name'
class
Dog(
object
):
name
=
"我是类变量"
def
__init__(
self
,name):
self
.name
=
name
@classmethod
def
eat(
self
):
print
(
"%s is eating"
%
self
.name)
d
=
Dog(
"ChenRonghua"
)
d.eat()
#执行结果
我是类变量
is
eating
属性方法
把一个方法变成一个静态属性
属性方法的作用就是通过@property把一个方法变成一个静态属性
class
Dog(
object
):
def
__init__(
self
,name):
self
.name
=
name
@property
def
eat(
self
):
print
(
" %s is eating"
%
self
.name)
d
=
Dog(
"ChenRonghua"
)
d.eat()
Traceback (most recent call last): ChenRonghua is eating File "/Users/jieli/PycharmProjects/python基础/自动化day7面向对象高级/属性方法.py", line 16, in <module> d.eat() TypeError: 'NoneType' object is not callable
正常调用如下
d = Dog("ChenRonghua")
d.eat
输出
ChenRonghua is eating
注:下面这个setter跟Java的setter方法一样,声明属性,setter,执行,顺序一模一样。
好吧,把一个方法变成静态属性有什么卵用呢?既然想要静态变量,那直接定义成一个静态变量不就得了么?well, 以后你会需到很多场景是不能简单通过 定义 静态属性来实现的, 比如 ,你想知道一个航班当前的状态,是到达了、延迟了、取消了、还是已经飞走了, 想知道这种状态你必须经历以下几步:
1. 连接航空公司API查询
2. 对查询结果进行解析
3. 返回结果给你的用户
因此这个status属性的值是一系列动作后才得到的结果,所以你每次调用时,其实它都要经过一系列的动作才返回你结果,但这些动作过程不需要用户关心, 用户只需要调用这个属性就可以,明白 了么?
class Flight(object): def __init__(self,name): self.flight_name = name def checking_status(self): print("checking flight %s status " % self.flight_name) return 1 @property def flight_status(self): status = self.checking_status() if status == 0 : print("flight got canceled...") elif status == 1 : print("flight is arrived...") elif status == 2: print("flight has departured already...") else: print("cannot confirm the flight status...,please check later") f = Flight("CA980") f.flight_status 航班查询
cool , 那现在我只能查询航班状态, 既然这个flight_status已经是个属性了, 那我能否给它赋值呢?试试吧
f = Flight("CA980")
f.flight_status
f.flight_status = 2
输出, 说不能更改这个属性,我擦。。。。,怎么办怎么办。。。
checking flight CA980 status flight is arrived... Traceback (most recent call last): File "/Users/jieli/PycharmProjects/python基础/自动化day7面向对象高级/属性方法.py", line 58, in <module> f.flight_status = 2 AttributeError: can't set attribute
当然可以改, 不过需要通过@proerty.setter装饰器再装饰一下,此时 你需要写一个新方法, 对这个flight_status进行更改。
class Flight(object): def __init__(self,name): self.flight_name = name def checking_status(self): print("checking flight %s status " % self.flight_name) return 1 @property def flight_status(self): status = self.checking_status() if status == 0 : print("flight got canceled...") elif status == 1 : print("flight is arrived...") elif status == 2: print("flight has departured already...") else: print("cannot confirm the flight status...,please check later") @flight_status.setter #修改 def flight_status(self,status): status_dic = { : "canceled", :"arrived", : "departured" } print("\033[31;1mHas changed the flight status to \033[0m",status_dic.get(status) ) @flight_status.deleter #删除 def flight_status(self): print("status got removed...") f = Flight("CA980") f.flight_status f.flight_status = 2 #触发@flight_status.setter del f.flight_status #触发@flight_status.deleter
注意以上代码里还写了一个@flight_status.deleter, 是允许可以将这个属性删除
反射
hasattr(obj,name_str) , 判断一个对象obj里是否有对应的name_str字符串的方法
getattr(obj,name_str), 根据字符串去获取obj对象里的对应的方法的内存地址
setattr(obj,'y',z), is equivalent to ``x.y = v''
delattr
通过字符串映射或修改程序运行时的状态、属性、方法, 有以下4个方法
def getattr(object, name, default=None): # known special case of getattr """ getattr(object, name[, default]) -> value Get a named attribute from an object; getattr(x, 'y') is equivalent to x.y. When a default argument is given, it is returned when the attribute doesn't exist; without it, an exception is raised in that case. """ pass getattr(object, name, default=None)
判断object中有没有一个name字符串对应的方法或属性
def setattr(x, y, v): # real signature unknown; restored from __doc__ """ Sets the named attribute on the given object to the specified value. setattr(x, 'y', v) is equivalent to ``x.y = v''
def delattr(x, y): # real signature unknown; restored from __doc__ """ Deletes the named attribute from the given object. delattr(x, 'y') is equivalent to ``del x.y'' """ delattr(x, y)
class Foo(object): def __init__(self): self.name = 'wupeiqi' def func(self): return 'func' obj = Foo() # #### 检查是否含有成员 #### hasattr(obj, 'name') hasattr(obj, 'func') # #### 获取成员 #### getattr(obj, 'name') getattr(obj, 'func') # #### 设置成员 #### setattr(obj, 'age', 18) setattr(obj, 'show', lambda num: num + 1) # #### 删除成员 #### delattr(obj, 'name') delattr(obj, 'func') 反射代码示例
实例:
def bulk(self): print("%s is yelling...." %self.name) class Dog(object): def __init__(self,name): self.name = name def eat(self,food): print("%s is eating..."%self.name,food) d = Dog("NiuHanYang") choice = input(">>:").strip() if hasattr(d,choice): getattr(d,choice) else: setattr(d,choice,bulk) #d.talk = bulk func = getattr(d, choice) func(d)
结果:
>>:tyt
NiuHanYang is yelling....
动态导入模块
import importlib __import__('import_lib.metaclass') #这是解释器自己内部用的 #importlib.import_module('import_lib.metaclass') #与上面这句效果一样,官方建议用这个