[that_guy_iain]

Not knowing Python, but I have a feeling things like this weren't as well known back in 2010 and the reason they're so well known is from people doing it at sites like Digg and then telling everyone that's a really bad idea. There are so many things that I know now for programming that were pretty much unknown 10-years ago because no one had really encountered them in a large scale setup.

[biorach]

Nah, this has been very well known since decades and is very easy to spot.

[ubercore]

Yeah this is covered in pretty much every style guide, tutorial, and reference. And is an easy screener in an interview. I'm also surprised anyone using Python as more than a toy experiment had this issue, especially in such a critical service.

[_qxau]

I've worked on a lot of Python as a hobbyist and student, much of it in real world use - probably at least 100kloc - and I've never encountered this. Where is this information? I'm worried that I'm missing some other "obvious" things. I've of course run into python's shallow vs deep copies, but I don't remember default values being shared between invocations.

[ubercore]

If you do a search for "python common gotchas" it's almost certain to come up, usually pretty prominently.