Instance Method

An instance method is a function defined within a class that operates on an individual object (instance) of that class. It is the default method type in Python and is characterized by accepting a reference to the calling instance as its first parameter, conventionally named self.

When an instance method is accessed via an object, Python automatically binds the method to that specific instance, creating a bound method. During invocation, the Python interpreter implicitly passes the instance reference to the self parameter, granting the method access to the instance namespace (its attribute dictionary, __dict__).

class Blueprint:
    # Definition: 'self' is the mandatory first parameter
    def instance_method(self, value):
        # Accessing and mutating the instance namespace
        self.state = value
        return self.state


# Instantiation
obj = Blueprint()


# Invocation: Python implicitly passes 'obj' as the 'self' argument
obj.instance_method(42) 


# The above invocation is semantically equivalent to:
Blueprint.instance_method(obj, 42)

Technical Characteristics

• Implicit Argument Passing: While self must be explicitly declared in the method signature, it is omitted during standard instance-level invocation. Evaluating instance.method returns a bound method object, which is then invoked directly with the remaining arguments.
• State Access: Through the self reference, instance methods possess read and write access to instance attributes (self.attribute) and can invoke other instance methods (self.other_method()).
• Class Access: Instance methods can traverse up to the class namespace using the __class__ attribute (e.g., self.__class__.class_attribute), allowing them to read or modify class-level state.
• Descriptor Protocol: Instance methods are implemented via Python’s descriptor protocol. Functions defined in a class dictionary have a __get__ method. When accessed via an instance, __get__ returns a bound method object wrapping both the underlying function and the instance. When accessed directly via the class (e.g., Blueprint.instance_method), it simply returns the standard function object.

Master Python with Deep Grasping Methodology!

Learn More