Python C api函数重载

Question

我有许多C函数接受不同的参数，例如

foo_i(int a)

foo_c(char c)

有没有可能在pythoncapi中重载这些函数？你知道吗

我尝试使用下表中的方法：

static PyMethodDef test_methods[] = {
    {"foo", (PyCFunction)foo_i, METH_VARARGS, "int"},
    {"foo", (PyCFunction)foo_c, METH_VARARGS, "char"},
    {NULL, NULL, 0, NULL}
};

但是当我从python调用foo时，我总是使用表底部的函数。你知道吗

关于如何在python c-api中使用foo（）调用foo i（）和foo c（）有什么想法吗？你知道吗

谢谢！你知道吗

Answer 1

要么给它们不同的Python级别的名称，要么编写一个包装函数来检查提供的参数并将其分派给正确的“real”函数。Python本身不直接支持基于参数类型重载函数。你知道吗

如果您想要为您编写包装器，您可以看看pybind11，它确实允许您尝试的重载（它是通过引擎盖下的类型检查包装器来实现的，所以它只是语法上的糖分，而不是行为上的改变）。你知道吗

未测试示例代码：

static PyObject*
foo_wrapper(PyObject *self, PyObject *arg)
{
    Py_buffer view;
    Py_ssize_t ival;

    // Check for/handle length 1 bytes-like object (bytes, bytearray, small mmap, etc.)
    if (PyObject_GetBuffer(arg, &view, PyBUF_SIMPLE) == 0) {
        if (view.len != 1) {
             PyErr_Format(PyExc_ValueError, "Must receive exactly one byte, got %zd", view.len);
             PyBuffer_Release(&view);
             return NULL;
        }
        foo_c(((char*)view.buf)[0]);
        Py_RETURN_NONE; // Or convert return from foo_c if it exists
    }

    // Check for/handle integer-like object that fits in C int
    PyErr_Clear(); // Ignore error for objects not supporting buffer protocol
    ival = PyNumber_AsSsize_t(arg, PyExc_ValueError);
    if (PyErr_Occurred()) {
        if (PyErr_ExceptionMatches(PyExc_TypeError)) {
            // Replace with general error message about both accepted argument types,
            // since only reporting error from int conversion might confuse folks
            PyErr_Format(PyExc_TypeError, "Argument must be length 1 bytes-like object or integer; received %R", Py_TYPE(arg));
        }
        return NULL;
    }

    // Check valid range (Py_ssize_t often larger than int)
    if (ival < INT_MIN or ival > INT_MAX) {
        return PyErr_Format(PyExc_ValueError, "Integer must be in range [%d-%d]; received %zd", INT_MIN, INT_MAX, ival);
    }

    foo_i((int)ival);
    Py_RETURN_NONE; // Or convert return from foo_i if it exists
}

static PyMethodDef test_methods[] = {
    {"foo", (PyCFunction)foo_wrapper, METH_O, "Wrapper for foo_c and foo_i"},
    {NULL, NULL, 0, NULL}
};