动态语言的定义：动态编程语言是高级程序设计语言的一个类别，在计算机科学领域已被广泛应用。

它是一类在执行时能够改变其结构的语言：比如新的函数、对象、甚至代码能够被引进，已有的函数能够被删除或是其它结构上的变化。

动态语言眼下很具有活力。

众所周知的ECMAScript（JavaScript）便是一个动态语言。除此之外如PHP、Ruby、Python等也都属于动态语言，而C、C++等语言则不属于动态语言。----来自维基百科

你是不是有过给class里面变量赋值却发现程序没达到自己预期结果的遭遇？是不是本来赋值给class.abc却赋给了class.abd？这事实上是动态语言惹的“祸”！

【博主曾经玩的是java】我们先来试着玩一玩

>>> class Person():def __init__(self, name = None, age = None):self.name = nameself.age = age>>> P = Person("The_Third_Wave", "24")
>>> 

在这里，我们定义了1个类Person，在这个类里，定义了两个初始属性name和age。可是人还有性别啊。假设这个类不是你写的是不是你会尝试訪问性别这个属性呢？

>>> P.sexuality = "male"
>>> P.sexuality
'male'
>>> 

这时候就发现问题了，我们定义的类里面没有sexuality这个属性啊！

怎么回事呢？

这就是动态语言的魅力和坑！这里实际上就是动态给实例绑定属性！所以博主“当年”从java转python被“坑”（无知啊）过！

我们再看下一个样例

>>> P1 = Person("Wave", "25")
>>> P1.sexualityTraceback (most recent call last):File "<pyshell#21>", line 1, in <module>P1.sexuality
AttributeError: Person instance has no attribute 'sexuality'
>>> 

我们尝试打印P1.sexuality，发现报错，P1没有sexuality这个属性。----给P这个实例绑定属性对P1这个实例不起作用！

那我们要给全部的Person的实例加上sexuality属性怎么办呢？答案就是直接给Person绑定属性！

>>>> Person.sexuality = None
>>> P1 = Person("Wave", "25")
>>> print P1.sexuality
None
>>> 

我们直接给Person绑定sexuality这个属性。重行实例化P1后，P1就有sexuality这个属性了！

那么function呢？怎么绑定？

>>> class Person():def __init__(self, name = None, age = None):self.name = nameself.age = agedef eat(self):print "eat food">>> def run(self, speed):print "Keeping moving, the speed is %s km/h" %speed>>> P = Person("The_Third_Wave", "24")
>>>
KeyboardInterrupt
>>> P.run()Traceback (most recent call last):File "<pyshell#5>", line 1, in <module>P.run()
AttributeError: Person instance has no attribute 'run'
>>> P.eat()
eat food
>>> import types
>>> Person.run = types.MethodType(run, None, Person)
>>> P.run(180)
Keeping moving, the speed is 180 km/h
>>> 

绑定我们了解了，可是怎么删除呢？

请看下面样例首先给的是属性的真删：

>>> P.name
'The_Third_Wave'
>>> P.sexTraceback (most recent call last):File "<pyshell#32>", line 1, in <module>P.sex
AttributeError: Person instance has no attribute 'sex'
>>> setattr(P, "sex", "male") # 増
>>> P.sex
'male'
>>> delattr(P, "name") # 删
>>> P.nameTraceback (most recent call last):File "<pyshell#36>", line 1, in <module>P.name
AttributeError: Person instance has no attribute 'name'
>>> 

加入方法呢？

>>> class Person():def __init__(self, name = None, age = None):self.name = nameself.age = agedef eat(self):print "eat food">>> P = Person("The_Third_Wave", "24")
>>> P.eat()
eat food
>>> P.run()Traceback (most recent call last):File "<pyshell#41>", line 1, in <module>P.run()
AttributeError: Person instance has no attribute 'run'
>>> def run(self, speed):print "Keeping moving, the speed is %s" %speed>>> setattr(P, "run", run)
>>> P.run(360)Traceback (most recent call last):File "<pyshell#45>", line 1, in <module>P.run(360)
TypeError: run() takes exactly 2 arguments (1 given)
>>> P.run(1, 360)
Keeping moving, the speed is 360
>>> 

删除

>>> delattr(P, "run")
>>> P.run()Traceback (most recent call last):File "<pyshell#48>", line 1, in <module>P.run()
AttributeError: Person instance has no attribute 'run'
>>> 

通过以上样例能够得出一个结论：相对于动态语言。静态语言具有严谨性！

所以，玩动态语言的时候。小心动态的坑！

那么怎么避免这样的情况呢？请使用__slots__，可是我的是2.7.6版本号。測试是不行的！代码例如以下：

>>> class Person():__slots__ = ("location", "run")def __init__(self, name = None, age = None):self.name = nameself.age = agedef eat(self):print "eat food">>> P = Person()
>>> P.sexTraceback (most recent call last):File "<pyshell#3>", line 1, in <module>P.sex
AttributeError: Person instance has no attribute 'sex'
>>> P.sex = "male"
>>> 

详细原因是什么呢。本来是准备请等待更新：ing...的

BUT，我多写了个object就出来了。

。。这可真是个神坑！

soga！

>>> class Person(object):__slots__ = ("location", "run")def __init__(self, name = None, age = None):self.name = nameself.age = agedef eat(self):print "eat food">>> P = Person()Traceback (most recent call last):File "<pyshell#12>", line 1, in <module>P = Person()File "<pyshell#11>", line 5, in __init__self.name = name
AttributeError: 'Person' object has no attribute 'name' # 顺便还发现了个注意事项：要预先定义的属性也要写到tuple里面！

>>> class Person(object): __slots__ = ("name", "age", "eat", "location", "run") def __init__(self, name = None, age = None): self.name = name self.age = age def eat(self): print "eat food" >>> P = Person() >>> P.sex = "male" Traceback (most recent call last): File "<pyshell#16>", line 1, in <module> P.sex = "male" AttributeError: 'Person' object has no attribute 'sex' >>> P.location = "china" >>> P.location 'china' >>> def run(self, speed): print "Keeping moving, the speed is %s km/h" %speed >>> setattr(P, "run", run) >>> P.run(u"请注意这儿參数和上面有个样例不一样哦", 720) Keeping moving, the speed is 720 km/h >>>

顺便还发现了个注意事项：要预先定义的属性也要写到tuple里面。

临时写到这。不定期更新ing...

关于slots的demo原文：https://docs.python.org/2/reference/datamodel.html?highlight=__slots__#__slots__

本文由@The_Third_Wave原创。不定期更新。有错误请指正。

Sina微博关注：@The_Third_Wave

假设这篇博文对您有帮助，为了好的网络环境，不建议转载，建议收藏。假设您一定要转载，请带上后缀和本文地址。