February 20, 2014

Rogue "heta": How I learned about raw strings in Python.

I don't claim to be a python wizard. Yes, I use python almost every day, but I use it differently than C. I understand C well, or more accurately, I know enough about the language, compiler optimization, and processor architecture to be dangerous when it comes to getting a computer to do tricks. I honestly don't care so much about what the python interpreter is doing because if I'm running into performance are scalability problems, python gets ditched. It's my quick-and-dirty tool.

Well, yesterday things got ugly, and I mean that literally. I was setting axes on a plot generated using matplotlib, and I was met with this on my X-axis:
Hmmm. I don't remember having a "heta" variable. I do remember having a theta, however, so I assumed that I had simply mistyped my label:
Double hmmm. Matplotlib supports LaTeX in strings, and I take full advantage of this fact quite often. Now I know some greek letters don't exist in LaTeX. Or rather, some capital greek letters are not included as special LaTeX commands because they are equivalent to their roman versions (for example, \epsilon exists, but \Epsilon does not, but you can just as easily write E and be done with it). None of this, however, applies here, because lowercase and uppercase theta do exist, and I was writing the lowercase version anyways. Omicron is the only greek letter to have neither upper nor lowercase LaTeX commands.

Dead-set on thinking I had somehow screwed up my LaTeX invocation, it never occurred to me that it could be a python problem until I turned to the smart guy I always annoy when I'm being dumb. A couple minutes and surgical Google trips later, I discovered that I had somehow managed to overlook raw strings for over three years (when I first picked up python to replace perl). Instead of writing a single LaTeX command, I had inadvertently written a tab character (\t) dutifully followed by four LaTeX variables h, e, t, and a. In hindsight, this should've been an obvious oversight: perl and bash both use single quote and double quotes to distinguish between interpreted and uninterpreted strings.

A single r prefixing the string, and sure enough, my axes are back to greek, I'm a little less ignorant, and all is good.

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