pyenv-python

A pyenv shim for python that's much faster than pyenv.

Usage

This python shim, i.e., $CARGO_HOME/bin/python, loads much faster than pyenv's python shim, which is written in Bash.

This helps a lot when running CLI scripts in Python, since the time is takes to run the CLI script is often less than the time it takes pyenv to find python.

For example, with starship, python --version is run every time when you're in a Python directory to display the current Python version on the prompt, but if pyenv's python shim takes ~1 sec, it makes the prompt painfully slow. Using this python shim, the time for python --version is unnoticeable.

Fast Script Invocation

For all globally install programs, like through pip install, pyenv places a shim file in $PYENV_ROOT/shims, which is placed in $PATH.
This shim has to call the real script through pyenv, which makes every script startup very slow, adding up to 1 second to every script, even on simple --help commands.

As a solution, pyenv-python's python executable supports invoking scripts with no overhead. If python is symlinked to script, then when ./script is run, it calls python script, where script should be in the same directory as the real python. That is, if python is the real python executable, then ./script calls python "$(dirname "$(which python)")"/script.

Installed python scripts are normally installed in the same directory as python, so this makes it very easy to invoke scripts with no pyenv overhead.

This can also be done for other binaries not named python, such as python2 or python3.

Performance

On my local computer, $CARGO_HOME/bin/python --version runs about 23x faster than $PYENV_ROOT/shims/python --version.

pyenv-python on  master is 📦 v0.4.0 via 🦀 v1.53.0 took 8s
❯ hyperfine '$CARGO_HOME/bin/python --version' '$PYENV_ROOT/shims/python --version'
Benchmark #1: $CARGO_HOME/bin/python --version
  Time (mean ± σ):      11.6 ms ±   1.6 ms    [User: 1.0 ms, System: 10.3 ms]
  Range (min … max):    10.0 ms …  19.9 ms    120 runs

Benchmark #2: $PYENV_ROOT/shims/python --version
  Time (mean ± σ):     258.4 ms ±   6.3 ms    [User: 18.5 ms, System: 213.7 ms]
  Range (min … max):   249.1 ms … 273.3 ms    10 runs

Summary
  '$CARGO_HOME/bin/python --version' ran
   22.19 ± 3.09 times faster than '$PYENV_ROOT/shims/python --version'

Installation

It's just published to crates.io, so you need cargo from rustup to install it.

Then cargo install pyenv-python will install the python wrapper. For this python to wrap the pyenv python or the system python, $CARGO_HOME/bin must be before any other pythons in $PATH.

This python wrapper also supports a few other commands.

• python --path prints the path of the python or script that it will execute.
• python --dir prints the directory of the python or script that it will execute, i.e. dirname $(python --path).
• python --prefix prints the prefix directory of the python or script that it will execute, i.e. dirname $(python --dir). This is the same as what python -c 'import sys; print(sys.prefix)' prints.
• python --which prints what command will be run using which python, explaining why that python.

These extra commands aren't compatible with actual python, but they don't clash with any actual python commands, and they're very useful for inspection. Previously, there was a separate python-path executable that did what python --path now does, but having one executable is much simpler.