以xy坐标为例，定义一个类：
1 class Coordinate(object): 2 def __init__(self, x, y): 3 self.x = x 4 self.y = y 5 def distance(self, other): 6 x_diff_sq = (self.x - other.x)**2 7 y_diff_sq = (self.y - other.y)**2 8 return (x_diff_sq + y_diff_sq)**0.5 9 def __str__(self): 10 return "<" + str(self.x) + "," + str(self.y) + ">"
class Coordinate(object): 中，object为其继承的父类
__init__ ：构造函数，定义类中的属性；参数self代表对象本身，例如 c = Coordinate(3, 4) ，c作为self参数被输入构造函数中
__str__ ：print self
【Other special operators】https://docs.python.org/3/reference/datamodel.html#basic-customization
E.g., __add__ +, __sub__ -, __eq__ ==, __lt__ <, __len__ len(), ...
【Getters and Setters】
1 class Animal(object): 2 def __init__(self, age): 3 self.age = age 4 self.name = None 5 6 #getter 7 def get_age(self): 8 return self.age 9 def get_name(self): 10 return self.name 11 12 #setter 13 def set_age(self, newage): 14 self.age = newage 15 def set_name(self, newname="") 16 self.name = newname
Getters and setters should be used outside of class to access data attributes. Better use a.get_age() instead of a.age .
【Default Arguments】
1 def set_name(self, newname = ""): 2 self.name = newname
1 a.set_name() 2 print(a.get_name()) # prints "" 3 4 a.set_name("Harman") 5 print(a.get_name()) # prints "Harman"
【Class Variables and Instance Variables】
1 class Rabbit(Animal): 2 tag = 1 3 def __init__(self, age, parent1=None, parent2=None): 4 Animal.__init(self, age) 5 self.parent1 = parent1 6 self.parent2 = parent2 7 self.rid = Rabbit.tag 8 Rabbit.tag += 1
该例中， tag 为class variable，其变量值由该类的所有实例共享； self.rid 为instance variable，是每个实例独有的。