Can I add an instance method to a Python "Mock" object?

Question

I would like to create a mock.Mock() object, then add a method called session that acts like an instance method, which is passed a self reference to the mock object, allowing the method to add state to the mock object. Is this possible (without manually using types.MethodType, e.g., using mock's built-in API), or should I just find a way around it?

Note, I found this question, which is for Ruby and seems to cover something similar, if not the same thing. Unfortunately, I don't know Ruby very well at all.

Answer 1

If you want to enhance the capabilities of the mock.Mock class, just subclass Mock and add your own methods.

class MyMock(Mock):
    def session(self):
        # Save session data here?

The mock documentation explains that when a new mock is to be created, it will be the same type as the parent. This means that the session function will also be available on any other mocks which are created during mocking.

This doesn't cover the case where you need to dynamically attach a session function to an existing mock object.

Answer 2

mock_answer = Mock()

def session():
    mock_answer.b = 1

mock_answer.session = session
mock_answer.session()
print(mock_answer.b)  # 1

You don't need self actually.