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.

laike9m · Accepted Answer · 2016-01-08 02:58:51Z

6

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.

answered Jan 8, 2016 at 2:58

laike9m

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1 Comment

Matt Over a year ago

but if you need to use self you could use partial: from functools import partial and then mock_answer.session = partial(session, mock_answer)

Austin Phillips · Accepted Answer · 2013-01-21 01:03:41Z

4

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.

answered Jan 21, 2013 at 1:03

Austin Phillips

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1 Comment

orokusaki Over a year ago

Thanks, that actually works fine. Although the subclass mimicking the parent part doesn't prove useful in my case, it won't hurt anything.

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