Launch IPython directly from package, instead of from path

[stefanv]

It happens, sometimes, that an install from a different version of Python is on the path. That leads to some unexepected and hard to debug issues.

This uses the -P flag which requires Python 3.11 (EOL for 3.10 is June 2026).

[lucascolley]

thanks Stefan, tested with SciPy:

diff --git a/pixi.toml b/pixi.toml
index dbe3e87d0d..adb339bd20 100644
--- a/pixi.toml
+++ b/pixi.toml
@@ -143,9 +143,13 @@ features = ["build-deps", "run-deps", "test-deps", "scipy-openblas"]
 ### Default dependencies (included in all environments) ###

 [dependencies]
-spin = "*"
+# spin = "*"
 python = "*"

+[pypi-dependencies]
+spin.git = "https://github.com/stefanv/spin.git"
+spin.branch = "ipython-use-sys-exec"

scipy on 🎋 main [🔨] is 📦 v1.18.0.dev0 via 🐍 via 🧚 v0.63.2 took 33s
❯ pixi ls spin
Name  Version       Build  Size  Kind  Source
spin  0.16rc0.dev0               pypi  git+https://github.com/stefanv/spin.git?branch=ipython-use-sys-exec#8106c9966eb286e62c7d3756399bc50bf881c7d5

scipy on 🎋 main [🔨] is 📦 v1.18.0.dev0 via 🐍 via 🧚 v0.63.2 took 2s
❯ pixi run ipython
✨ Pixi task (build in build): spin build --setup-args=-Dblas=blas --setup-args=-Dlapack=lapack --setup-args=-Duse-g77-abi=true: (Build SciPy (default settings))
$ meson compile -j 8 -C build
INFO: autodetecting backend as ninja
INFO: calculating backend command to run: /Users/lucascolley/ghq/github.com/scipy/scipy/.pixi/envs/build/bin/ninja -C /Users/lucascolley/ghq/github.com/scipy/scipy/build -j 8
ninja: Entering directory `/Users/lucascolley/ghq/github.com/scipy/scipy/build'
[2/356] Generating subprojects/highs/highs/HConfig.h with a custom command
$ meson install --only-changed -C build --destdir ../build-install --tags=runtime,python-runtime,tests,devel --skip-subprojects
✨ Pixi task (ipython in ipython): spin ipython --no-build: (Launch IPython)
$ export PYTHONPATH="/Users/lucascolley/ghq/github.com/scipy/scipy/build-install/usr/lib/python3.14/site-packages"
💻 Launching IPython with PYTHONPATH="/Users/lucascolley/ghq/github.com/scipy/scipy/build-install/usr/lib/python3.14/site-packages"
$ /Users/lucascolley/ghq/github.com/scipy/scipy/.pixi/envs/ipython/bin/python3.14 -P -m IPython --ignore-cwd
Python 3.14.2 | packaged by conda-forge | (main, Dec  6 2025, 11:34:40) [Clang 20.1.8 ]
Type 'copyright', 'credits' or 'license' for more information
IPython 9.8.0 -- An enhanced Interactive Python. Type '?' for help.
Tip: You can use `%hist` to view history, see the options with `%history?`

In [1]: import scipy

In [2]: scipy.show_config()
/Users/lucascolley/ghq/github.com/scipy/scipy/build-install/usr/lib/python3.14/site-packages/scipy/__config__.py:166: UserWarning: Install `pyyaml` for better output
  warnings.warn("Install `pyyaml` for better output", stacklevel=1)
{
  "Compilers": {
    "c": {
      "name": "clang",
      "linker": "ld64",
      "version": "19.1.7",
      "commands": "/Users/lucascolley/ghq/github.com/scipy/scipy/.pixi/envs/build/bin/ccache, arm64-apple-darwin20.0.0-clang",

[stefanv]

Thanks for testing, @lucascolley! This has been driving me insane, since my local setup someone has Python injected from the wrong place.