Bound Methods, Unbound Methods, and Functions in Python: What\'s the Difference?

Bound Methods, Unbound Methods, and Functions: A Distinctive Trio in Python

In the realm of Python object manipulation, understanding the differences between functions, bound methods, and unbound methods is crucial. Let's embark on a journey to unravel their nuances.

What is a Function?

A function is essentially a self-contained code block that performs a specific task. It is created using the def or lambda statements. When a function is defined within a class, Python transforms it into an unbound method.

What is an Unbound Method?

An unbound method is a function attached to a class but not yet bound to a specific instance of that class. In Python 2, unbound methods are created when a function is inserted into a class statement. In Python 3, the concept of unbound methods has been eliminated.

What is a Bound Method?

A bound method is a function that has been bound to an instance of a class. When a bound method is accessed on a class instance, it automatically supplies the instance to the method as the first parameter.

Interconversion

• Function to Unbound Method: Use the types.MethodType class constructor: types.MethodType(function, None, class)
• Unbound Method to Bound Method: Access the unbound method on a class instance or use the get method: unbound_method.__get__(instance, class)
• Bound Method to Function: Retrieve the original function using the im_func attribute: bound_method.im_func

Practical Implications

The main difference between a function and an unbound method is that the latter knows which class it belongs to, while a function does not. This becomes evident when trying to call these methods without an appropriate instance.

Furthermore, binding a function to an instance fixes the first argument (self) to the instance, effectively replacing the bound method with an equivalent lambda function or partial function.

Conclusion

Understanding the distinctions between functions, unbound methods, and bound methods is essential for effective object manipulation in Python. Each of these forms serves a unique purpose, and their interconversion allows for the dynamic binding of methods to instances.

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