Sunday, February 25, 2007

Minimal Working Examples: How to, Why, and Who cares

When you have a problem and you rush to colleagues, or strangers on IRC and mailing lists, you've got to present a problem they'll want to help you fix, and with all the information they need to fix it. You can't give them information they dont need, because any extra work filing through your unrelated code is going to reduce the chances anyone will put in the time to help you.

We can state a few rules about seeking help with code.
  1. Ask the question clearly and don't be ambiguous about your intentions and requirements.
  2. If you need to include code, it needs to include all important context.
  3. Present the problem without reference to out-of-context issues.
Don't come in with a link to your entire body of code telling us it doesn't work. What doesn't work is asking for help like that. Besides telling us exactly how things don't work, and what they are doing compared to what you are expecting, you need to give us code that specifically and only demonstrates the problem directly at hand. This is our golden "Minimal Working Example", where "working" means that it works just enough to show us how its broken. You need to reproduce the situation causing your code to break, without showing us the environment your code is in when it breaks. That means taking code segments out of their modules and even out of the insides of functions, and surrounding them with just enough jumpstart to fail the same way it did in the original code.

Before you even get around to asking your question, you might solve it simply by isolating the problem into your example. When you remove the problem code from everything else, you can remove the distractions of everything else going on around it. You might remove another part of the code to reduce things to the minimal example, and suddenly find the problem gone, identifying the removed code as the source of your problems. If you think isolating test cases sounds familiar, then you know enough that I shouldn't have to tell you these minimal working examples should already exist in the form of your unit test suites. When something goes wrong, you should have already had a test to catch it, and added one if you didn't. If the problem can be isolated now, keep it isolated for later.

Remember what is important to your problem. If you can't figure out some particular pysqlite2 issue, and you're working with data your extracted from XML files grabbed from a remote server, you can bet the XML, HTTP, and all the logic to process it is not worth your time to show anyone. Your example only needs to show the data you have to push through SQL, and no one should need to see where its come from. If your components are more tightly woven, and separating them isn't possible or is even moderately difficult, then you have a serious design flaw and extracting the problem example has revealed away to clear up your code and likely solve many latent problems, all at once.

Once proper testing, documentation, and isolation have let you up the creek without a paddle, thats where community support comes in. Come to us with the example that tells us right away what the problem is, what its doing, and the obvious thing you think it should have done, instead. We can all run this code and approach it from the same direction as yourself, so we know exactly what your problem is and where to approach the solution.

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I write here about programming, how to program better, things I think are neat and are related to programming. I might write other things at my personal website.

I am happily employed by the excellent Caktus Group, located in beautiful and friendly Carrboro, NC, where I work with Python, Django, and Javascript.

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