Beware of defaults

I spent a good portion of yesterday staring at my Django test cases and whimpering.  No matter what I tried, no matter how thoroughly I flushed the database between each test case, state seemed to be persisting from test to test.  “How is this happening?” I howled to my computer.

It was only when I gave up and went to go celebrate my niece’s second birthday that the answer occurred to me.  I’d set a model field default to ‘{}’ instead of ‘dict’.

This is listed as a “common Python gotcha” but I’ve only ever run into it once before in approximately six years of coding in Python.  The previous time was in a job interview, which totally stymied me.  Luckily it also stymied the interviewer, and I got the job.