pydata

Keep Looking, Don't Settle

python class (1): class, object, attribute and method

一个简单的python的类的例子：

#encoding = utf-8
class Person(object):
 def __init__(self, name, age):
  #这儿self.name和self.age都是object的attributes
  self.name = name
  self.age = age
  print '%s has been born in' %(self.name)

p1 = Person('Johnny', 2001)
p2 = Person('Mary', 1987)

这时候如果打印p1而不是p1.name，只会打印出p1对象（内存地址）

怎么打印object的data？答案是转换成str
class Person(object):
 def __init__(self, name, age):
  self.name = name
  self.age = age
  print '%s has been born' %(self.name)
 def __str__(self):
  #这个时候class的调用会返回str
  return '%s is %s years old' %(self.name, self.age)

p1 = Person('Johnny', 20)
p2 = Person('Mary', 27)

print p1
print p2
添加一个 del method
class Person(object):
 def __init__(self, name, age):
  self.name = name
  self.age = age
  print '%s has been born' %(self.name)
 def __str__(self):
  #这个时候class的调用会返回str
  return '%s is %s years old' %(self.name, self.age)
 def __del__(self):
  #添加一个del method
  print '%s is deleted :(' %(self.name)

p1 = Person('Johnny', 20)
p2 = Person('Mary', 27)
print p1
print p2
del(p1)
del(p2)
class variable
class Person(object):
 population = 0  #注意不在__str__里面，也没有self在前面
 def __init__(self, name, age):
  self.name = name        #self定义的object variable，是object的attributes
  self.age = age
  print '%s has been born' %(self.name)
  Person.population += 1   #注意Person.，因为这是class variable
 def __str__(self):
  #这个时候class的调用会返回str
  return '%s is %s years old' %(self.name, self.age)
 def __del__(self):
  #添加一个del method
  print '%s is deleted :(' %(self.name)
  Person.population -= 1    #注意Person.，因为这是class variable
p1 = Person('Johnny', 20)
print Person.population
p2 = Person('Mary', 27)
print Person.population
print p1
print p2
del(p1)
print Person.population
del(p2)
print Person.population
class method or static method(好像python2.7不能运行通过，只能python3运行)
class Person:
    population = 0  #注意不在__str__里面，也没有self在前面
    def __init__(self, name, age):
        self.name = name        #self定义的object variable，是object的attributes
        self.age = age
        Person.population += 1   #注意Person.，因为这是class variable
    def __str__(self):
        #这个时候class的调用会返回str
        return '%s is %s years old' %(self.name, self.age)
    def __del__(self):
        #添加一个del method
        Person.population -= 1    #注意Person.，因为这是class variable
    def totalPop():     #注意括号里面没有self，所以跟object不相连
        print('There are {0} people in the world'.format(Person.population))

p1 = Person('Johnny', 20)
p2 = Person('Mary', 27)
Person.totalPop()   #这样没问题，因为是class method
p1.totalPop()  #会报错，因为不是object p1的method

reference: https://www.youtube.com/watch?v=gGMwx9JHpWc