What are the Differences between Bound, Unbound, and Static Methods in Python?

Class Method Differences in Python: Bound, Unbound, and Static

In Python, the distinction between bound, unbound, and static methods is crucial for effective class design.

Bound and Unbound Methods

Unlike most other object-oriented languages, Python class methods are not static by default. When a class instance calls a member function, it is translated into a call to the unbound method with the instance as the first argument. For instance, consider the following code:

class Test(object):
  def method_one(self):
    print "Called method_one"

Calling method_one on an instance a_test will result in:

a_test.method_one()
=> Test.method_one(a_test)

Static Methods

To define a static method that is invoked on the class rather than an instance, use the @staticmethod decorator. This decorator instructs the metaclass to create an unbound method. For example:

class Test(object):
    @staticmethod
    def method_two():
        print "Called method_two"

Now, both the instance and the class can invoke method_two:

a_test = Test()
a_test.method_one()
a_test.method_two()
Test.method_two()

Calling method_two without an instance will not raise an error, unlike method_one, which expects an instance to be bound to it.

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