uv has been fantastic to use for little side projects. Combining uv run with `uv tool run` AKA `uvx` means one can fetch, install within a VM, and execute Python scripts from Github super easily. No git clone, no venv creation + entry + pip install.
And uv is fast — I mean REALLY fast. Fast to the point of suspecting something went wrong and silently errored, when it fact it did just what I wanted but 10x faster than pip.
It (and especially its docs) are a little rough around the edges, but it's bold enough and good enough I'm willing to use it nonetheless.
I know there are real reasons for slow Python startup time, with every new import having to examine swaths of filesystem paths to resolve itself, but it really is a noticeable breath of fresh air working with tools implemented in Go or Rust that have sub-ms startup.
You don't have to import everything just to print the help. I try to avoid top-level imports until after the CLI arguments have been parsed, so the only import until then is `argparse` or `click`. This way, startup appears to be instant even in Python.
Example:
if __name__ == "__main__":
from myapp.cli import parse_args
args = parse_args()
# The program will exit here if `-h` is given
# Now do the heavy imports
from myapp.lib import run_app
run_app(args)
Another pattern, though, is that a top level tool uses pkg_resources and entry_points to move its core functionality out to verb plugins— in that case the help is actually the worst case scenario because not only do we have to scan the filesystem looking for what plugins are available, they all have to be imported in order to ask each for its help strings.
An extreme version of this is the colcon build tool for ROS 2 workspaces:
The Python startup latency thing makes sense, but I really don't understand why it would take `pyenv` a long time to print each line of its "usage" output (the one that appears when invoking it with `--help`) once it's already clearly in the code branch that does only that.
It feels like like it's doing heavy work between each line printed! I don't know any other cli tool doing that either.
The "slowness" and the utter insanity of trying to make a "works on my computer" Python program work on another computer pushed me to just rewrite all my Python stuff in Go.
About 95% of my Python utilities are now Go binaries cross-compiled to whatever env they're running in. The few remaining ones use (API) libraries that aren't available for Go or aren't mature enough for me to trust them yet.
I agree uv is amazing, but it's not a virtual machine, it's a virtual environment. It runs the scripts on top of your OS without any hardware virtualization. The virtual environment only isolates the Python dependencies.
not sure if OP will see this, but how does uv or uvx forgo `git clone` ? You still need to clone whatever you're trying to run, or am I missing something.
Is there a reason you didn’t explicitly pull in mkdocs as a dependency in that invocation? I guess uv will expose it/let you run it anyways due to the fact that it’s required by everything else you did specify.
And uv is fast — I mean REALLY fast. Fast to the point of suspecting something went wrong and silently errored, when it fact it did just what I wanted but 10x faster than pip.
It (and especially its docs) are a little rough around the edges, but it's bold enough and good enough I'm willing to use it nonetheless.