Variance of generic types in Python

Although I’ve been using Python 3.12 in production for nearly a year, one neat feature in the typing module that escaped me was the @override decorator. Proposed in PEP-6981, it’s been hanging out in typing_extensions for a while. This is one of those small features you either don’t care about or get totally psyched over. I’m definitely in the...

This morning, someone on Twitter pointed me to PEP 5621, which introduces __getattr__ and __dir__ at the module level. While __dir__ helps control which attributes are printed when calling dir(module), __getattr__ is the more interesting addition. The __getattr__ method in a module works similarly to how it does in a Python class. For example:...

I always get tripped up by Docker’s different mount types and their syntax, whether I’m stringing together some CLI commands or writing a docker-compose file. Docker’s docs cover these, but for me, the confusion often comes from how “bind” is used in various contexts and how “volume” and “bind” sometimes get mixed up in the documentation. Here’s...

I was fiddling with graphlib in the Python stdlib and found it quite nifty. It processes a Directed Acyclic Graph (DAG), where tasks (nodes) are connected by directed edges (dependencies), and returns the correct execution order. The “acyclic” part ensures no circular dependencies. Topological sorting is useful for arranging tasks so that each...

Besides retries, circuit breakers1 are probably one of the most commonly employed resilience patterns in distributed systems. While writing a retry routine is pretty simple, implementing a circuit breaker needs a little bit of work. I realized that I usually just go for off-the-shelf libraries for circuit breaking and haven’t written one from...