Pybind11中C++引用传递列表对象修改不生效问题的解决方案

// mymodule.cpp
#include <pybind11/pybind11.h>
#include <vector>

namespace py = pybind11;

// 定义一个简单的C++类 A
class A {
public:
    int n = 0;
    double val = 0.0;
    A() = default; // 默认构造函数
};

// 函数B：按值传递A对象
inline void B_by_value(A a) {
    a.n = 1;
    a.val = 0.1;
}

// 函数B：按引用传递A对象
inline void B_by_reference(A& a) {
    a.n = 2;
    a.val = 0.2;
}

// Pybind11绑定代码
PYBIND11_MODULE(mymodule, m) {
    m.doc() = "Pybind11 example for reference passing";

    py::class_<A>(m, "A")
        .def(py::init<>())
        .def_readwrite("n", &A::n)
        .def_readwrite("val", &A::val);

    m.def("B_by_value", &B_by_value, "Modifies A by value (no change in Python)");
    m.def("B_by_reference", &B_by_reference, "Modifies A by reference (changes reflected in Python)");
}

import mymodule

# 1. 按值传递
a_val = mymodule.A()
print(f"Before B_by_value: a_val.n={a_val.n}, a_val.val={a_val.val}")
mymodule.B_by_value(a_val)
print(f"After B_by_value: a_val.n={a_val.n}, a_val.val={a_val.val}")
# 结果：a_val 未被修改

# 2. 按引用传递
a_ref = mymodule.A()
print(f"Before B_by_reference: a_ref.n={a_ref.n}, a_ref.val={a_ref.val}")
mymodule.B_by_reference(a_ref)
print(f"After B_by_reference: a_ref.n={a_ref.n}, a_ref.val={a_ref.val}")
# 结果：a_ref 被成功修改

// 接着上面的mymodule.cpp
// ... (A类和py::class_<A>绑定代码不变)

// 函数C：按引用传递 A 对象列表
inline void C_list_by_reference(std::vector<A>& alist) {
    for (auto& a : alist) {
        a.n = 3;
        a.val = 0.3;
    }
}

// Pybind11绑定代码
PYBIND11_MODULE(mymodule, m) {
    // ... (A类和B_by_value, B_by_reference绑定不变)
    m.def("C_list_by_reference", &C_list_by_reference, "Modifies list of A by reference (elements might not update in Python)");
}

import mymodule

# 创建一个包含A对象的Python列表
list_a = [mymodule.A(), mymodule.A()]
print(f"Before C_list_by_reference:")
for i, obj in enumerate(list_a):
    print(f"  list_a[{i}]: n={obj.n}, val={obj.val}")

mymodule.C_list_by_reference(list_a)

print(f"After C_list_by_reference:")
for i, obj in enumerate(list_a):
    print(f"  list_a[{i}]: n={obj.n}, val={obj.val}")
# 结果：list_a 中的元素未被修改

// 接着上面的mymodule.cpp
// ... (A类和py::class_<A>绑定代码不变)

// 函数D：按引用传递 A 对象指针列表
inline void D_list_by_pointer_reference(std::vector<A*>& alist_ptrs) {
    for (A* a_ptr : alist_ptrs) {
        if (a_ptr) { // 检查指针是否为空
            a_ptr->n = 4;
            a_ptr->val = 0.4;
        }
    }
}

// Pybind11绑定代码
PYBIND11_MODULE(mymodule, m) {
    // ... (A类和B_by_value, B_by_reference, C_list_by_reference绑定不变)
    m.def("D_list_by_pointer_reference", &D_list_by_pointer_reference, "Modifies list of A using pointers (changes reflected in Python)");
}

import mymodule

# 创建一个包含A对象的Python列表
list_a_solution = [mymodule.A(), mymodule.A()]
print(f"Before D_list_by_pointer_reference:")
for i, obj in enumerate(list_a_solution):
    print(f"  list_a_solution[{i}]: n={obj.n}, val={obj.val}")

mymodule.D_list_by_pointer_reference(list_a_solution) # Pybind11会自动将Python列表中的A对象转换为A*

print(f"After D_list_by_pointer_reference:")
for i, obj in enumerate(list_a_solution):
    print(f"  list_a_solution[{i}]: n={obj.n}, val={obj.val}")
# 结果：list_a_solution 中的元素被成功修改