Python meta-programming (meta-class instance)

This instance is a meta-class instance, and the function is to record the class name of the subclass, and to display the class name of the subclass in a tree-like structure.

Registerclasses inherits from type, which provides the ability to create a collection of childrens for a class in the __init__ interface, and to save the class name to the collection of childrens of the corresponding parent class tuple.

The __str__ printing method and the __iter__ iterative method are also defined, in which:

The __iter__ method returns the childrens collection of the class name and enters the elements therein.

While Sharp inherits from Registerclasses, when for s in Sharp:print S, the inherited __iter__ method is called.

Class Round (Shape): Pass
Class Square (Shape): Pass
Class triangular (Shape): Pass
Class Boxy (Shape): Pass

In the above operation, Round,square,triangular,boxy Initializes a collection of childrens,
At the same time, it adds its own class name to the collection of childrens of the shape meta-class.

Class Circle (Round): Pass
Class Ellipse (Round): Pass

In the above operation, Circle,ellipse Initializes a collection of childrens,
At the same time, all of their class names are added to the Round,shape childrens collection,

The reason: Round's parent class is shape, so Circle,ellipse has two parent classes.

The code is as follows:

#!/usr/bin/env python
# Encoding:utf-8
"""
@author:
@contract:
@file: homework5_1.py
@time: 2016/10/26 14:22
"""
Class Registerclasses (Type):
Def __init__ (CLS, name, bases, Atts):
Super (Registerclasses, CLS). __INIT__ (name, bases, Atts)

#创建一个集合, so inheriting the meta-class, there will be a collection of childrens
Cls.childrens = set ()

#将把当前的子类保存到父类中去
For base in bases:
If Hasattr (base, ' childrens '):
Base.childrens.add (CLS)

#classmethod, called on class object
def __iter__ (CLS):
Return iter (Cls.childrens)

def __str__ (CLS):
If Len (Cls.childrens) > 0:
return cls.__name__ + ":" + ",". Join ([sc.__name__ for SC in CLS])
Else
Return cls.__name__

Class Shape (object):
__metaclass__ = registerclasses

Print "---------------------"
Class Round (Shape): Pass
Class Square (Shape): Pass
Class triangular (Shape): Pass
Class Boxy (Shape): Pass
Print Shape
Print "---------------------"
Class Circle (Round): Pass
Class Ellipse (Round): Pass
Print Shape
Print "---------------------"
For S in Shape: #Iterator over subclasses (Def __str__ (CLS):)
Print S
Print "---------------------"
For CLS in Shape.childrens:
If Len (Cls.childrens) > 0:
Print cls.__name__ + ":" + ",". Join ([sc.__name__ for SC in CLS])
Else
Print cls.__name__

The output is as follows:

---------------------
Shape:triangular, Boxy, Square, Round
---------------------
Shape:triangular, Boxy, Square, Round
---------------------
Triangular
Boxy
Square
Round:ellipse, Circle
---------------------
Triangular
Boxy
Square
Round:ellipse, Circle

Python meta-programming (meta-class instance)