Generates CPython bindings for [Interoptopus](https://github.com/ralfbiedert/interoptopus).

## Usage

Assuming you have written a crate containing your FFI logic called `example_library_ffi` and
want to generate **CPython bindings** for Python 3.7+, follow the instructions below.

#### Inside Your Library

Add [**Interoptopus**](https://crates.io/crates/interoptopus) attributes to the library you have
written, and define an inventory function listing all symbols you wish to export. An overview of all
supported constructs can be found in the
[**reference project**](https://github.com/ralfbiedert/interoptopus/tree/master/reference_project/src).

```rust
use interoptopus::{ffi_function, ffi_type, Inventory, InventoryBuilder, function};

#[ffi_type]
#[repr(C)]
pub struct Vec2 {
    pub x: f32,
    pub y: f32,
}

#[ffi_function]
#[no_mangle]
pub extern "C" fn my_function(input: Vec2) -> Vec2 {
    input
}

pub fn my_inventory() -> Inventory {
    InventoryBuilder::new()
        .register(function!(my_function))
        .inventory()
}
```


Add these to your `Cargo.toml` so the attributes and the binding generator can be found
(replace `...` with the latest version):

```toml
[lib]
crate-type = ["cdylib", "rlib"]

[dependencies]
interoptopus = "..."
interoptopus_backend_cpython = "..."
```

Create a unit test in `tests/bindings.rs` which will generate your bindings when run
with `cargo test`. In real projects you might want to add this code to another crate instead:

```rust
use interoptopus::util::NamespaceMappings;
use interoptopus::{Error, Interop};

#[test]
fn bindings_cpython_cffi() -> Result<(), Error> {
    use interoptopus_backend_cpython::{Config, Generator};

    let library = example_library_ffi::my_inventory();

    Generator::new(Config::default(), library)
        .write_file("bindings/python/example_library.py")?;

    Ok(())
}
```

Now run `cargo test`.

If anything is unclear you can find a [**working sample on Github**](https://github.com/ralfbiedert/interoptopus/tree/master/examples/hello_world).

#### Generated Output

The output below is what this backend might generate. Have a look at the [`Config`] struct
if you want to customize something. If you really don't like how something is generated it is
easy to [**create your own**](https://github.com/ralfbiedert/interoptopus/blob/master/FAQ.md#new-backends).

```python
from __future__ import annotations
import ctypes
import typing

T = typing.TypeVar("T")
c_lib = None

def init_lib(path):
    """Initializes the native library. Must be called at least once before anything else."""
    global c_lib
    c_lib = ctypes.cdll.LoadLibrary(path)
    c_lib.my_function.argtypes = [Vec2]
    c_lib.my_function.restype = Vec2


def my_function(input: Vec2) -> Vec2:
    return c_lib.my_function(input)


TRUE = ctypes.c_uint8(1)
FALSE = ctypes.c_uint8(0)


class Vec2(ctypes.Structure):
    # These fields represent the underlying C data layout
    _fields_ = [
        ("x", ctypes.c_float),
        ("y", ctypes.c_float),
    ]

    def __init__(self, x: float = None, y: float = None):
        if x is not None:
            self.x = x
        if y is not None:
            self.y = y

    @property
    def x(self) -> float:
        return ctypes.Structure.__get__(self, "x")

    @x.setter
    def x(self, value: float):
        return ctypes.Structure.__set__(self, "x", value)

    @property
    def y(self) -> float:
        return ctypes.Structure.__get__(self, "y")

    @y.setter
    def y(self, value: float):
        return ctypes.Structure.__set__(self, "y", value)

```