> callable(callable)
True
> callable(1)
False
> 1()
Traceback (most recent call last):
File "<pyshell#5>", line 1, in <module>
1()
TypeError: 'int' object is not callable
>

> class A: #定义类A
  pass

> callable(A) #类A是可调用对象
True
> a = A() #调用类A
> callable(a) #实例a不可调用
False
> a() #调用实例a失败
Traceback (most recent call last):
 File "<pyshell#31>", line 1, in <module>
  a()
TypeError: 'A' object is not callable


> class B: #定义类B
  def __call__(self):
    print('instances are callable now.')

    
> callable(B) #类B是可调用对象
True
> b = B() #调用类B
> callable(b) #实例b是可调用对象
True
> b() #调用实例b成功
instances are callable now.