1 python中的任何一条数据都是对象，每个对象都由3部分组成：标识、类型和值。

对象的标识代表该对象在内存中的存储位置 不可更改，对象的类型表明它可以拥有的数据和值的类型。在对象中，可变类型的值可以更改，不可变类型的值不能更改

2 类允许定义一组对象，并将它们封装到一个方便的空间中。

3 使用dir函数可以列举出一个对象的所有属性和方法 dir(fridge)

以下划线开关的名称是对象的私有属性，它们是不可见的。即不能直接使用它们

 函数内置到一个对象中时，它叫做这个对象的方法

函数len就是利用方法__len__工作的：函数len向这个内置方法询问对象的长度。对象的设计者可定义长度的计算方式，使得对于定义了__len__方法的任何对象，内置函数len都能够正确运行

4 通过 class 关键字声明类 并在后面紧跟一个名称来完成

class Fridge:

"""this class implements a fridge """

类的名称以大写字母开头是惯例。当类的名称有多个单词时，每个词以大写字母开头以方便阅读。

5使用一对圆括号调用Fridge类，可以创建一个对象：f=Fridge()

class Fridge:
""" this class is a fridge
methods: has(food_name[,quantity]) checks if the string food_name is in the fridge. quantity will be set to 1 if you do not specify a number.
has_various(foods) check if enough of every food in the dictionary is in the fridge
add_one(food_name) adds a single food_name to the fridge
add_many(food_dict) adds a whole dictionary filled with food
get_one(food_name) - takes out a single food_name from the fridge
get_many(food_dict) - takes out a whole dictionary worth of food.
get_ingredients(food) - if passed an object that has the __ingredients__ method,get_many will invoke this to get the list of ingredients.

"""
def __init__(self,items={}):
"""optionally pass in an initial dictionary of items """
if type(items)!=type({}):
raise TypeError("Fridge requires a dictionary but was given %s"%type(items))
self.items=items
return
def _add_multi(self,food_name,quantity):
""" adds more than one of a food item.returns the numer of items
added. this should only be used internally,after the type checking has been done """
if (not food_name in self.items):
self.items[food_name]=0
self.items[food_name]=self.items[food_name]+quantity
def add_one(self,food_name):
"""
add_one(food_name)-adds a single food_name to the fridge returns true
raise a TypeError is food_name is not a string."""
if type(food_name)!=type(""):
raise TypeError("add_one requires a string,given a %s" %type(food_name))
else:
self._add_multi(food_name,1)
return True
def add_many(self,food_dict):
""" adds a whole dictionary filled with food as keys and quantities as values.returns a dictionary with the removed food. raises a TypeError if food_dict is not a dictionary. returns false if there is not enough food in the fridge."""
if type(food_dict)!=type({}):
raise TypeError("add_many requires a dictionary got a %s"%food_dict)
for item in food_dict.keys():
self._add_multi(item,food_dict[item])
return

运行文件后 使用 类

>>> f=Fridge({"eggs":6,"milk":4,"cheese":3})
>>> f.items
{'eggs': 6, 'milk': 4, 'cheese': 3}
>>> f.add_one("grape")
True
>>> f.items
{'eggs': 6, 'milk': 4, 'cheese': 3, 'grape': 1}
>>> f.add_many({"mushroom":5,"tomato":4})
>>> f.add_many({"mushroom":5,"tomato":4})
>>> f.items
{'eggs': 6, 'milk': 4, 'cheese': 3, 'mushroom': 10, 'tomato': 8}

 使用记事本的tab 长度与 在shell中的tab长度不一致，则在记事本中写入程序后 ，在shell中再写入后面的程序，运行报错

保持接口行为不变的能力叫做类的稳定性

 

class Omelet:
""" this class creates an omelet object. an omelet can be in one of two states:ingredients, or cooked. an omelet object has the following interfaces:
get_kind() returns a string with the type of omelet
set_kind(kind) sets the omelet to be the type named
set_new_kind(kind,ingredients) lets you create an omelet
mix() gets called after all the ingredients are gathered from the fridge
cook() cooks the omelet"""

def __init__(self,kind="cheese"):
""" this initialized the omelet class to default to cheese omelet. other methods"""
self.set_kind(kind)
return
def __ingredients__(self):
"""internal method to be called on by a fridge or other objects that need to act on ingredients"""
return self.needed_ingredients
def get_kind(self):
return self.kind
def set_kind(self,kind):
possible_ingredients=self.__known_kinds(kind)
if possible_ingredients==False:
return False
else:
self.kind=kind
self.needed_ingredients=possible_ingredients
def set_new_kind(self,name,ingredients):
self.kind=name
self.needed_ingredients=ingredients
return
def __known_kinds(self,kind):
if kind=="cheese":
return{"eggs":2,"milk":1,"cheese":1}
elif kind=="mushroom":
return {"eggs":2,"milk":1,"cheese":1,"mushroom":2}
elif kind=="onion":
return {"eggs":2,"milk":1,"cheese":1,"onion":1}
else:
return False
def get_ingredients(self,fridge):
self.from_fridge=fridge.get_ingredients(self)
def mix(self):
for ingredient in self.from_fridge.keys():
print("Mixing %d %s for the %s omelet"%(self.from_fridge[ingredient],ingredient,self.kind))
self.mixed=True
def make(self):
if self.mixed==True:
print("Cooking the %s omelet!"%self.kind)
self.cooked=True

运行文件 使用类制作

>>> o=Omelet("cheese")
>>> f=Fridge({"cheese":5,"milk":4,"eggs":12})

>>> o.get_ingredients(f)
>>> o.mix()
Mixing 2 eggs for the cheese omelet
Mixing 1 milk for the cheese omelet
Mixing 1 cheese for the cheese omelet
>>> o.make()
Cooking the cheese omelet!