Scenario 3 — Grouped types in a single subpackage module¶

You're here if: you're building a collection of related filter types — Fir, Biquad, Equalizer — and you want from my_filters.filter import Fir, Biquad rather than a separate top-level import for each.

Use this when multiple related Python types should share one .so and import from a common subpackage path. Each type still has its own independent C library; the module is the Python grouping unit only.

1. Scaffold the project and module together¶

just-makeit new my_filters --module filter
cd my_filters

--module is repeatable — --module osc --module env scaffolds two modules in one command. Each module is an empty slot; types are added with just-makeit object.

Alternatively, scaffold the project first and add the module separately:

just-makeit new my_filters
cd my_filters
just-makeit module filter

2. Add types¶

just-makeit object fir \
    --module filter \
    --state "coeffs:float[16]" \
    --state "delay:float _Complex[16]" \
    --state "gain:float:1.0"

just-makeit object biquad \
    --module filter \
    --arg-type float \
    --return-type float \
    --state "b0:double:1.0" \
    --state "b1:double:0.0" \
    --state "b2:double:0.0" \
    --state "a1:double:0.0" \
    --state "a2:double:0.0" \
    --state "w1:double:0.0" \
    --state "w2:double:0.0"

Each just-makeit object call:

• Creates the C library (_core.h, _core.c, C test, C benchmark)
• Fully regenerates the module's filter_ext.c, CMakeLists.txt, and __init__.py

After both objects:

# src/my_filters/filter/__init__.py — generated
from .filter import Fir, Biquad

__all__ = ["Fir", "Biquad"]

Types within a module may have different --arg-type/--return-type. Here Fir processes float _Complex and Biquad processes float.

3. Implement¶

Edit native/inc/fir/fir_core.h and native/inc/biquad/biquad_core.h to fill in the _step stubs, exactly as in Scenarios 1 and 2.

4. Build and test¶

make && make test

CMake builds one .so (filter.cpython-*.so) inside src/my_filters/filter/, linking both fir_core and biquad_core OBJECT libraries. CTest runs test_fir_core and test_biquad_core.

5. Install¶

pip install .

The wheel contains one .so for the filter subpackage rather than one .so per type.

6. Use from Python¶

import numpy as np
from my_filters.filter import Fir, Biquad

fir = Fir(gain=1.0)
bq  = Biquad(b0=1.0)

Both types are fully independent — separate create/destroy lifecycles, each with its own step, steps, reset, and context manager support.

7. Add a third type later¶

just-makeit object iir --module filter --state "gain:float:1.0"

filter_ext.c, CMakeLists.txt, and __init__.py are all regenerated from the complete object list. Fir and Biquad are unaffected.

8. Install¶

pip install .

The wheel is rebuilt with iir included.

Standalone object vs module object — when to use which¶

Both workflows produce a lib<project>.so C library that supports cmake --install, pkg-config, and CMake find_package.