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Quickstart

Quickstart#

This page shows how to get results with litgen in 5 minutes, without setting up a full repo.
You will generate Python stub code and C++ binding code from a simple header.

To actually compile and import the bindings, please use the Litgen Template.

Step 1: Install litgen#

pip install litgen

or, for the latest development version:

pip install "litgen@git+https://github.com/pthom/litgen"

Step 2: Write a small C++ header#

// file: mylib.h
#pragma once

inline int add(int a, int b) { return a + b; }

struct Point {
    int x = 0;
    int y = 0;
};

Step 3: Run litgen#

# file: generate.py
import litgen

options = litgen.LitgenOptions()
gen = litgen.generate_code_for_file(options, "mylib.h")

print("===================================")
print("=== Generated stub code (.pyi) ===")
print("===================================")
print(gen.stub_code)
print()
print("===================================")
print("=== Generated pydef code (.cpp) ===")
print("===================================")
print(gen.pydef_code)

Run it:

python generate.py

Step 4: Inspect the output#

Stub file (Python declarations, .pyi):

def add(a: int, b: int) -> int:
    pass

class Point:
    x: int = 0
    y: int = 0
    def __init__(self, x: int = 0, y: int = 0) -> None:
        """Auto-generated default constructor with named params"""
        pass

Pydef file (C++ binding code, .cpp):

m.def("add",
    add, py::arg("a"), py::arg("b"));


auto pyClassPoint =
    py::class_<Point>
        (m, "Point", "")
    .def(py::init<>([](
    int x = 0, int y = 0)
    {
        auto r_ctor_ = std::make_unique<Point>();
        r_ctor_->x = x;
        r_ctor_->y = y;
        return r_ctor_;
    })
    , py::arg("x") = 0, py::arg("y") = 0
    )
    .def_readwrite("x", &Point::x, "")
    .def_readwrite("y", &Point::y, "")
    ;

(exact output may vary depending on options and backend)

Step 5: A small tweak (optional)#

You can adjust LitgenOptions to control what gets generated.
For example, to exclude functions whose name starts with _:

options.fn_exclude_by_name__regex = r"^_"

Or to add a custom method, add this before calling generate_code_for_file:

options.custom_bindings.add_custom_bindings_to_class(
    "Point",
    stub_code="def norm(self) -> float: ...",
    pydef_code="LG_CLASS.def(\"norm\", [](const Point& p){ return sqrt(p.x*p.x + p.y*p.y); });"
)

and you will get this stub:

class Point:
    x: int = 0
    y: int = 0
    def __init__(self, x: int = 0, y: int = 0) -> None:
        """Auto-generated default constructor with named params"""
        pass

    def norm(self) -> float: ...

Next steps#

You now know how to generate stubs and C++ binding code.

To compile these bindings into an importable Python module (with CMake, scikit-build, packaging, CI, etc.), please use the Litgen Template.

Continue reading the User Guide for more details on how to customize the generation.

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