浅析 python 对象模型huntzhan(詹昊恂)

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导言

• 讲座主题与价值

• Python 中底层对象的结构

• 加深对 Python 的理解, 提前踩坑, 提升编码效率

• 关键问题: 在 Python 中,

• 什么是对象?

• 有几种对象? 它们之间是什么关系?

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讲座的结构

• 必要的概念讲解: OOP术语/概念, 自省, Python 相关属性与函数

• <class 'type'> 与 <class 'object'>

• new-style class 与 classic class

• 对象模型的结构

• 总结

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prerequisite一些基础概念

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OOP Relationships

• superclass-subclass

relationships, 继承关系, 实线

• superclass/baseclass, 基类

• subclass/derived class, 派生类

• class-instance, 实例关系, 虚线

• class, 类

• instance, 实例

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Python Example

class Super:

pass

class Sub(Super):

pass

class C:

pass

cobj = C()

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type/class

• type/class 宽松定义

• represent abstract data types in programs

• can be subclassed(继承)

• can be instantiated(实例化)

• class(类) 等价于 type(类型), in Python >= 2.2

• 下文会混用 class 与 type, 不必惊慌, XD

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object, 对象

• object 宽松定义. object 包含的信息

• Type

• Base Classes

• Identity, see id()

• Value

• Attributes

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Everything is an object!

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Everything Is an object!

• object 包括

• type object

• non-type object(instance)

• besides, instance

• can not be subclassed

• can not be instantiated

features type non-type

Type O O

Base

ClassesO X

Identity O O

Value X O

Attributes O O

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Introspection, 自省

• type introspection is the ability of a program to

examine the type or properties of an object at

runtime.

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• examine the type

• type(object)

• object.__class__

• isinstance(object, classinfo)

• object.__bases__

• issubclass(class, classinfo)

• examine the properties

• dir([object])

• hasattr(object, name)

class Super:

pass

class Sub(Super):

pass

class C:

pass

Reflection, 反射

• the ability to manipulate the values, meta-data,

properties and/or functions of an object at runtime

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• globals(), locals()

• object attribute manipulation

• understand data model, attributes and methods

• setattr, getattr, delta

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<class 'type'> 与 <class 'object'>

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• <class ‘type’>: type of all classes

• <class ‘object’>: base class of all *other* classes

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烧脑一刻

• 2a: If X is an instance of A, and A is a subclass of B, then

X is an instance of B as well.

• 2b: If B is an instance of M, and A is a subclass of B,

then A is an instance of M as well.

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烧脑一刻

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more built-in classes

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new object by

instantiation

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new object by class

definition

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new object by function definition

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new-style class 与 classic class

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classic class

• classes defined with a class

statement that does not have

a built-in object amongst its

bases: either because it has

no bases, or because all of its

bases are classic classes

themselves - applying the

definition recursively.

• deprecated in Python 3.

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对象模型中的位置

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new-style class

• Introduced in Python 2.2.

• <class ‘type’>

• <class 'object'>

• “to remove most of the

differences between built-in

types and user-defined

classes”.

• always defines a new-style

class instead of classic

class!

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对象模型的结构

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结构层次

• object:

• type object

• metaclass

• class

• non-type object(instance)

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• 为什么要区分 metaclass 与 class?

• 控制 class 的创建过程, 支持更高层次的抽象手段

• 什么时候使用 metaclass ?

• “Never (as long as you're asking this question

anyway :)”

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创建 metaclass

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总结

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什么是 object (对象)?

• Everything is an object!

• object 包含的 5 个信息.

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object cheat sheet

• dri(cls): 包含 cls 以及其派生类(derived class)的集合.

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reading list• http://www.cafepy.com/article/python_types_and_objects/python_ty

pes_and_objects.html

• https://www.python.org/download/releases/2.2.3/descrintro/

• https://en.wikipedia.org/wiki/Type_introspection#Python

• https://en.wikipedia.org/wiki/Type_system#Static_and_dynamic_typ

e_checking_in_practice

• https://docs.python.org/3.4/library/types.html

• https://docs.python.org/3.5/reference/datamodel.html

• https://www.python.org/doc/newstyle/

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