I've been bitten by that exactly once. In order to track it down, I had to tear out pieces of my program to issolate where it is, to the point where I was worki

I've been bitten by that exactly once. In order to track it down, I had to tear out pieces of my program to issolate where it is, to the point where I was working with a single function that did nothing other than mutate a dict that was a default value and print said value; and code that called it twice.