python动态添加类方法_Python 动态添加类方法
習題：
1. Shape基類，要求所有子類都必須提供面積的計算，子類有三角形、矩形、圓。
2. 上題圓類的數據可序列化
第一種方法：使用Mixin多繼承組合的方式，混入其它類的屬性和方法
第二種方法：使用裝飾器裝飾類，動態添加屬性和方法
實例：
import math
import json
import msgpack
import pickle
class Shape:
"""防止直接調用父類的area方法"""
@property
def area(self):
raise NotImplementedError(‘基類未實現‘)
class Triangle(Shape):
"""三角形"""
def __init__(self,a,b,c):
self.a = a
self.b = b
self.c = c
@property
def area(self):
p = (self.a+self.b+self.c)/2
return math.sqrt(p*(p-self.a)*(p-self.b)*(p-self.c))
class Rectangle(Shape):
"""矩形"""
def __init__(self,width,height):
self.width = width
self.height = height
@property
def area(self):
return self.width * self.height
def SerializableCircle(cls):
""" 1.裝飾器為類動態添加dumps方法"""
# print(cls)
def dumps(self,t=‘json‘):
if t == ‘json‘:
return json.dumps(self.__dict__)
elif t == ‘msgpack‘:
return msgpack.packb(self.__dict__)
elif t == ‘pickle‘:
with open(‘dump.txt‘,‘wb‘) as f:
return pickle.dump(self.__dict__,f)
else:
raise NotImplementedError(‘沒有實現的序列化‘)
cls.dumps = dumps
return cls
@SerializableCircle # Circle=SerializableCircle(Circle)
class Circle(Shape):
"""圓形"""
def __init__(self,radius):
self.radius = radius
@property
def area(self):
return (self.radius ** 2) * math.pi
# def dumps(self,t=‘json‘):
# if t == ‘json‘:
# return json.dumps(self.__dict__)
# elif t == ‘msgpack‘:
# return msgpack.packb(self.__dict__)
# elif t == ‘pickle‘:
# with open(‘dump.txt‘,‘wb‘) as f:
# return pickle.dump(self.__dict__,f)
# else:
# raise NotImplementedError(‘沒有實現的序列化‘)
# sc = Circle(4)
# sc.dumps(‘pickle‘)
class SerializableMixin:
"""序列化"""
def dumps(self,t=‘json‘):
if t == ‘json‘:
return json.dumps(self.__dict__)
elif t == ‘msgpack‘:
return msgpack.packb(self.__dict__)
elif t == ‘pickle‘:
with open(‘dump.txt‘,‘wb‘) as f:
return pickle.dump(self.__dict__,f)
else:
raise NotImplementedError(‘沒有實現的序列化‘)
def loads(self,t=‘json‘):
pass
class SerializableCircleMixin(SerializableMixin,Circle):
""" 2.Mixin組合為類動態添加dumps方法"""
pass
shapes = [Triangle(3,4,5), Rectangle(3,4), Circle(4)]
for s in shapes:
print(‘The area of {} = {}‘.format(s.__class__.__name__,s.area))
#Mixin
scm = SerializableCircleMixin(4)
print(scm.area)
s = scm.dumps(‘msgpack‘)
print(s)
#裝飾器
sc = Circle(4)
s = sc.dumps(‘json‘)
print(s)
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