How Can I Add a Method to a Specific Object Instance in Python?

Adding a Method to an Existing Object Instance: A Guide for Python

While generally discouraged, the addition of a method to an object instance can be necessary under certain circumstances. In Python, the distinction between functions and bound methods is crucial for this process.

Bound methods are linked to a specific instance, which is automatically provided as the first argument upon invocation. Conversely, class-level callables remain unbound, enabling dynamic class definition modifications.

To attach a method to the entire class, simply update its definition:

def fooFighters(self):
    print "fooFighters"

A.fooFighters = fooFighters

This method becomes available to all instances, including previously defined ones.

Attaching a method to an individual instance presents a challenge. Assigning it directly to the instance does not bind it, leading to an error when calling.

To resolve this, utilize the MethodType function from the types module:

import types
a.barFighters = types.MethodType(barFighters, a)

Bound methods only affect the specific instance they are attached to, leaving other class instances untouched. For further insights, explore topics such as descriptors and metaclass programming.

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