Now that we have a pretty good idea of doctests, the next question is: how does this fit into the TDD process? Remember, in the TDD process, we write the test first, and then the implementation later. Do doctests fit in with this process?

In a way, yes. Doctests are not a particularly good fit for doing TDD for single methods. The unittest module is a better choice for those. Where doctest shines is at package-level interaction. Explanations interspersed with examples really bring out interaction between different modules and classes within the package. Such doctests can be written out at the beginning, giving a high-level overview of how we want the package as a whole to work. These tests will fail. As individual classes and methods are written, the tests will start to pass.