An Unfoolish Consistency: Introducing PEP8 to a legacy codebase

by Rob Galanakis on 25/04/2014

Consistency with this style guide is important. Consistency within a project is more important. Consistency within one module or function is most important.

The EVE source code, being initially developed before PEP8 existed, was based on Microsoft’s C++ style. Mostly this is manifested in UpperCamelCase function and method names, mixedCase parameter and variable names, and file headers and class/method delimiters. There was also a style guide that was probably larger than PEP8 (though included a bit more than basic style).

Today, most new code is PEP8 compliant. “What!?” I hear you say. “A foolish consistency is the hobgoblin of little minds!” I agree, and I’ll get back to that at the end. But first, what was involved in introducing PEP8?

The move started when I asked my team if anyone wanted to keep using the headers and delimiters. No one did. So we took out the headers and delimiters before we did any modifications to a file.

A while later, I asked all the programmers on the project if anyone felt strongly about keeping the existing style. No one did. So we started writing new packages with PEP8. The rationale was that our code was already calling code using lowercase_underscore in the stdlib, so it’d be no different for that same code to call a relatively independent, though still project-related, library.

Yet a while later, I started slipping some PEP8 code into modules or packages that weren’t PEP8. I was worried people would get upset. No one did.

And finally, in preparing some basic utility libraries for usage on other projects, I converted the function and method names to PEP8. This involved find-and-replace or CamelCase aliases. I bet you can guess who cared about these “superfluous” edits, or objected to the fact that parameter and variable names remained mixedCase? No one did.

Emerson’s quote “a foolish consistency is the hobgoblin of little minds” is often used as a reason to not change existing code to PEP8, or introduce it into a non-PEP8 codebase. But the quote means the opposite. Foolish consistency” is being unable to change your mind because it would contradict something you’ve believed or said. So PEP8 has it so right but so wrong: the foolish consistency is to keep things the way they are, even though we know what the right thing to do is.*


* I would recommend introducing PEP8 incrementally. I also suggest keeping things backwards compatible when it is more prudent, such as if the changes are expansive, or you do not control all the code. I also don’t suggest being a stylistic nitpicker when it comes to non-functional aspects such as line length. There may also be times to break the rules (a class that behaves like a function, or function that behaves like a class def). As always, good sense should be applied when considering any viewpoints on this blog.

rob.galanakis@gmail.com

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