py

The py spell wires a Python project's tooling into a magusfile through uv. Tests, linting (ruff), and formatting run as uv run subcommands so they resolve from the project's locked environment.

Runtime name: py (source spells/python/)

Version probe: python3 --version

Passing arguments to ops

Every op is invoked as py["<op>"](ctx, opts?). The first argument is the target's context, which is what carries the execution environment; the optional options map shapes the command itself:

Working directory and environment are NOT options: they ride the context, as py["<op>"](ctx.withCwd("sub")) and py["<op>"](ctx.withEnv({"CGO_ENABLED": "0"})). Only the context reaches the cache key, so an option-table cwd or env would change what the tool did while the key said otherwise - passing either as an option is an error.

Charms (the :charm suffix, e.g. magus run test:rw) are orthogonal: they patch the base argv, while these options add to it. See Charms.

pytest

Command: uv run pytest

debug

Appends -v.

[
  {
    "op": "add",
    "path": "/-",
    "value": "-v"
  }
]

Example

// pytest runs the suite via `uv run`; here filtered to tests matching a keyword,
// so `magus run test` forks `uv run pytest -k integration`. The debug charm
// (`magus run test:debug`) adds -v.
import "magus";
import "magus/spell/py";

magus\project({ "spells": [py] });

export fun test(ctx: magus\Context, args: [str]) > void {
    py["pytest"](ctx, { "args": ["-k", "integration"] });
}

ruff-check

Command: uv run ruff check .

debug

Appends -v.

[
  {
    "op": "add",
    "path": "/-",
    "value": "-v"
  }
]

gha

Inserts --output-format=github.

[
  {
    "op": "add",
    "path": "/3",
    "value": "--output-format=github"
  }
]

rw

Inserts --fix.

[
  {
    "op": "add",
    "path": "/3",
    "value": "--fix"
  }
]

Example

// ruff-check lints via uv run ruff; the rw charm autofixes, gha annotates in CI.
import "magus";
import "magus/spell/py";

magus\project({ "spells": [py] });

export fun lint(ctx: magus\Context, args: [str]) > void {
    py["ruff-check"](ctx);
}

ruff-format

Command: uv run ruff format --check .

rw

Drops --check.

[
  {
    "op": "remove",
    "path": "/3"
  }
]

Example

// ruff-format checks formatting; the rw charm (magus run format:rw) rewrites in place.
import "magus";
import "magus/spell/py";

magus\project({ "spells": [py] });

export fun format(ctx: magus\Context, args: [str]) > void {
    py["ruff-format"](ctx);
}

scip

scip is the reserved op that runs the Python SCIP indexer for the knowledge graph. The indexer is a PATH binary (install it with mise, not as a project dep), so the op forks it directly. magus injects MAGUS_SYMBOL_INDEX with the cache destination, so the index never lands in the tree; scip-python writes there via --output. Run through sh so the env var expands.

Command: sh -c scip-python index . --output "$MAGUS_SYMBOL_INDEX"

uv-build

build/clean are uv's own subcommands; pytest and ruff are tools uv merely runs, so they are named after the tool (pytest, ruff-check), not the uv run wrapper.

Command: uv build

Example

// Wire uv-build into a build target: magus run build forks uv build.
import "magus";
import "magus/spell/py";

magus\project({ "spells": [py] });

export fun build(ctx: magus\Context, args: [str]) > void {
    py["uv-build"](ctx);
}

uv-clean

Command: uv clean

Example

// Wire uv-clean into a clean target: magus run clean forks uv clean.
import "magus";
import "magus/spell/py";

magus\project({ "spells": [py] });

export fun clean(ctx: magus\Context, args: [str]) > void {
    py["uv-clean"](ctx);
}