Python - Anonymous Class and Objects


Python's built-in type() function returns the class that an object belongs to. In Python, a class, both a built-in class or a user-defined class are objects of type class.

Example

class myclass:
   def __init__(self):
      self.myvar=10
      return
      
obj = myclass()

print ('class of int', type(int))
print ('class of list', type(list))
print ('class of dict', type(dict))
print ('class of myclass', type(myclass))
print ('class of obj', type(obj))

It will produce the following output

class of int <class 'type'>
class of list <class 'type'>
class of dict <class 'type'>
class of myclass <class 'type'>

The type() has a three argument version as follows −

Syntax

newclass=type(name, bases, dict)

Using above syntax, a class can be dynamically created. Three arguments of type function are −

  • name − name of the class which becomes __name__ attribute of new class

  • bases − tuple consisting of parent classes. Can be blank if not a derived class

  • dict − dictionary forming namespace of the new class containing attributes and methods and their values.

We can create an anonymous class with the above version of type() function. The name argument is a null string, second argument is a tuple of one class the object class (note that each class in Python is inherited from object class). We add certain instance variables as the third argument dictionary. We keep it empty for now.

anon=type('', (object, ), {})

To create an object of this anonymous class −

obj = anon()
print ("type of obj:", type(obj))

The result shows that the object is of anonymous class

type of obj: <class '__main__.'>

Example

We can also add instance variables and instance methods dynamically. Take a look at this example −

def getA(self):
   return self.a
obj = type('',(object,),{'a':5,'b':6,'c':7,'getA':getA,'getB':lambda self : self.b})()
print (obj.getA(), obj.getB())

It will produce the following output

5 6
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