Python Duck Typing

We know that in Python, the data type of the variables is not explicitly declared. This does not mean that Python variables do not have a type. Every variable or object in Python has a type and the type is implicitly assigned depending on the purpose for which the variable is used.



Python variables are names or tags that point to memory locations where data is stored. They are not worried about which data we are going to store. So, if 'x' is a variable, we can make it refer to an integer or a string as shown in the previous examples. We can conclude two points from this discussion:


  1. Python's type system is 'strong' because every variable or object has a type that we can check with the type() function.

  2. Python's type system is 'dynamic' since the type of a variable is not explicitly declared, but it changes with the content being stored.

Similarly, if we want to call a method on an object, we do not need to check the type of the object and we do not need to check whether that method really belongs to that object or not. For example, take a method call_talk() that accepts an object (or instance).


def call_talk(obj):

obj.talk()


The call_talk() method is receiving an object 'obj' from outside and using this object, it is invoking (or calling) talk() method.


A Python program to invoke a method on an object without knowing the type (or class) of the object.


A Python program to call a method that does not appear in the object passed to the method.


So in Python, we never worry about the type (class) of objects. The object type is distinguished only at runtime. If 'it walks like a duck and talks like a duck, it must be a duck'-this is the principle we follow. This is called duck typing. From the previous example, we can understand that the behavior of the talk() method is changing depending on the object type.This is an example for polymorphism of methods.


We can rewrite Program where we can check whether the object passed to the call_talk() method has the method that is being invoked or not. This is done by rewriting the method as:



In the preceding code, we are checking whether the object has a method or not with the help of hasattr() function. This function is written in the form of:


hasattr(object, attribute)


Here,'attribute'may be amethod or variable.


If it is found in the object (i.e. in the class to which the object belongs) then this method returns True, else False.


Checking the object type (or class) in this manner is called 'strong typing'.


A Python program to check the object type to know whether the method exists in the object or not.