I've been using DejaVu Sans (proportional) for programming (including Python) for the last few months, and found it very easy to get used to. There are just a few glyphs that could be adjusted to line up better (closing braces in JS/PHP are a few px off), or in the case of quotation marks, two single quotes render the same as one double quote. I've started editing DejaVu (it's OSS) to correct these small number of issues, I don't think they are insurmountable.