Are we losing out on performance of the actual installed thing, then? (I'm not 100% clear on .pyc files TBH; I'm guessing they speed up start time?)
My first cynical instinct is to say that this is uv making itself look better by deferring the costs to the application, but it's probably a good trade-off if any significant percentage of the files being compiled might not be used ever so the overall cost is lower if you defer to run time.
Sure, but you pay that hit either way. Real-world performance is always usage based: the assumption that uv makes is that people run (i.e. import) packages more often than they install them, so amortizing at the point of the import machinery is better for the mean user.
(This assumption is not universal, naturally!)
(The key part being that 'less common' doesn't mean a non-trivial amount of time.)
I just read the thread and use Python, I can't comment on the % speedup attributed to uv that comes from this optimization.
If it was a optional toggle it would probably become best practice to activate compilation in dockerfiles.
It seems like tons of people are creating container images with an installer tool and having it do a bunch of installations, rather than creating the image with the relevant Python packages already in place. Hard to understand why.
For that matter, a pre-baked Python install could do much more interesting things to improve import times than just leaving a forest of `.pyc` files in `__pycache__` folders all over the place.
I would bet on a subset for pretty much any non-trivial package (i.e. larger than one or two user facing modules). And for those trivial packages? Well they are usually small, so the cost is small as well. I'm sure there are exceptions: maybe a single gargantuan module thst consists of autogenerated FFI bindings for some C library or such, but that is likely the minority.
My Docker build generating the byte code saves it to the image, sharing the cost at build time across all image deployments — whereas, building at first execution means that each deployed image instance has to generate its own bytecode!
That’s a massive amplification, on the order of 10-100x.
“Well just tell it to generate bytecode!”
Sure — but when is the default supposed to be better?
Because this sounds like a massive footgun for a system where requests >> deploys >> builds. That is, every service I’ve written in Python for the last decade.
They do.
> Are we losing out on performance of the actual installed thing, then?
When you consciously precompile Python source files, you can parallelize that process. When you `import` from a `.py` file, you only get that benefit if you somehow coincidentally were already set up for `multiprocessing` and happened to have your workers trying to `import` different files at the same time.
Unfortunately, it typically doesn't work out as well as you might expect, especially given the expectation of putting `import` statements at the top of the file.