bindings/python/src/_slice.c

	// Copyright (c) 2025-present The Bitcoin Core developers
	// Distributed under the MIT software license, see the accompanying
	// file COPYING or http://www.opensource.org/licenses/mit-license.php.

	#include "_slice.h"

	struct Self
	{
	PyObject_HEAD
	PyObject* seq;
	Py_ssize_t start;
	Py_ssize_t step;
	Py_ssize_t length;
	};

	static void dealloc(struct Self* self)
	{
	Py_DECREF(self->seq);
	Py_TYPE(self)->tp_free((PyObject*)self);
	}

	static Py_ssize_t length(struct Self const* self)
	{
	return self->length;
	}

	static PyObject* item(struct Self const* self, Py_ssize_t idx)
	{
	if (idx < 0 \|\| idx >= self->length) {
	PyErr_SetString(PyExc_IndexError, "index out of range");
	return NULL;
	}

	PySequenceMethods const* seq = Py_TYPE(self->seq)->tp_as_sequence;
	return seq->sq_item(self->seq, self->start + (idx * self->step));
	}

	static PySequenceMethods as_sequence = {
	.sq_length = (lenfunc)length,
	.sq_item = (ssizeargfunc)item,
	};

	static PyMappingMethods as_mapping = {
	.mp_length = (lenfunc)length,
	.mp_subscript = Slice_subscript,
	};

	PyTypeObject Slice_Type = {
	PyVarObject_HEAD_INIT(NULL, 0)
	.tp_name = "btck._Slice",
	.tp_basicsize = sizeof(struct Self),
	.tp_dealloc = (destructor)dealloc,
	.tp_as_sequence = &as_sequence,
	.tp_as_mapping = &as_mapping,
	.tp_flags = Py_TPFLAGS_DEFAULT,
	.tp_doc = "Lazy slice view of a sequence",
	};

	PyObject* Slice_subscript(PyObject* self, PyObject* arg)
	{
	PySequenceMethods const* seq = Py_TYPE(self)->tp_as_sequence;

	if (PyIndex_Check(arg)) {
	Py_ssize_t idx = PyNumber_AsSsize_t(arg, PyExc_IndexError);
	if (idx == -1 && PyErr_Occurred()) {
	return NULL;
	}
	if (idx < 0) {
	idx += seq->sq_length(self);
	}
	return seq->sq_item(self, idx);
	}

	if (PySlice_Check(arg)) {
	Py_ssize_t start, stop, step; // NOLINT(readability-isolate-declaration)
	if (PySlice_Unpack(arg, &start, &stop, &step) < 0) {
	return NULL;
	}

	struct Self* slice = PyObject_New(struct Self, &Slice_Type);
	if (slice == NULL) {
	return NULL;
	}

	slice->seq = Py_NewRef(self);
	slice->start = start;
	slice->step = step;
	slice->length = PySlice_AdjustIndices(seq->sq_length(self), &start, &stop, step);

	return (PyObject*)slice;
	}

	return PyErr_Format(PyExc_TypeError, "indices must be integers or slices, not %.200s", Py_TYPE(arg)->tp_name);
	}

btck