判断对象是否可被调用：能被调用的对象是一个callable 对象

>>> callable(str)
True
>>> callable(int)
True

# Student 对象实例目前不可调用：

>>> class Student():
        def __init__(self,id,name):
            self.id = id
            self.name = name

>>> xiaoming = Student(id='1',name='xiaoming')
>>> callable(xiaoming)
False

# 如果 xiaoming能被调用 , 需要重写Student类的__call__方法：

>>> class Student():
      def __init__(self,id,name):
        self.id = id
        self.name = name

# 此时调用 xiaoming():

>>> xiaoming = Student('001','xiaoming')
>>> xiaoming()
I can be called
my name is xiaoming