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    "# Python 与 C++ 语言\n",
    "C++ 语言是对 C 语言的扩展，两者常被视为一个整体，集成于同一编译环境之中——你只须将一个 C 程序的文件后缀由 .c 改为 .cpp，它就成了 C++ 程序。C++ 在 C 语法之上增加了许多高级特性，运行效率相近而更加灵活多变，因此其应用领域也更为广阔。\n",
    "![Cpp.png](https://upload-images.jianshu.io/upload_images/10829283-d4429d8ec4124538.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)\n",
    "\n",
    "下面来看一个 C++ 程序示例 myclass.cpp——这段源码首先包含了 C++ 标准库的“输入输出流”头文件，能够更方便地读入数据并打印结果（可以对照之前 C 代码的输入输出方式）；随后定义了一个“圆”类，用一个私有成员变量表示半径，并用两个公有成员函数分别计算面积和周长（可以对照 Python 中定义类及创建实例的语法）：\n",
    "```\n",
    "#include <iostream>\n",
    "const double PI = 3.14159;\n",
    "class Circle\n",
    "{\n",
    "  private:\n",
    "    double r;\n",
    "  public:\n",
    "    Circle(double r_)\n",
    "    {\n",
    "        r = r_;\n",
    "    }\n",
    "    double area()\n",
    "    {\n",
    "        return PI * r * r;\n",
    "    }\n",
    "    double perimiter()\n",
    "    {\n",
    "        return 2 * PI * r;\n",
    "    }\n",
    "};\n",
    "int main()\n",
    "{\n",
    "    double r;\n",
    "    std::cout << \"请输入圆的半径：\";\n",
    "    std::cin >> r;\n",
    "    Circle c = Circle(r);\n",
    "    std::cout << \"圆的面积为：\" << c.area() << std::endl;\n",
    "    std::cout << \"圆的周长为：\" << c.perimiter() << std::endl;\n",
    "}\n",
    "```\n",
    "\n",
    "你已经知道 Python 能够使用 C/C++ 共享库，实际上 C/C++ 还可以编写 Python 专用共享库也就是扩展模块——让我们来尝试一下，首先新建文件 mymath.cpp：\n",
    "```\n",
    "/* C/C++编写Python扩展模块示例\n",
    "需要包含Python提供的头文件，例如VSCode应添加以下配置\n",
    "\"C_Cpp.default.includePath\": [\"~/miniconda3/include/python3.7m\"],\n",
    "*/\n",
    "#include <Python.h>\n",
    "/* 计算斐波纳契数列的项 */\n",
    "int cFib(int n)\n",
    "{\n",
    "    if (n < 2)\n",
    "        return n;\n",
    "    return cFib(n - 1) + cFib(n - 2);\n",
    "}\n",
    "/* Python函数 */\n",
    "static PyObject *fib(PyObject *self, PyObject *args)\n",
    "{\n",
    "    int n;\n",
    "    if (!PyArg_ParseTuple(args, \"i\", &n))\n",
    "        return NULL;\n",
    "    return Py_BuildValue(\"i\", cFib(n));\n",
    "}\n",
    "/* Python方法列表 */\n",
    "static PyMethodDef module_methods[] = {\n",
    "    {\"fib\", fib, METH_VARARGS, \"calculates the fibonachi number\"},\n",
    "    {NULL, NULL, 0, NULL}};\n",
    "/* Python模块 */\n",
    "static struct PyModuleDef mymath =\n",
    "    {\n",
    "        PyModuleDef_HEAD_INIT,\n",
    "        \"mymath\",        /* 模块名 */\n",
    "        \"mymath module\", /* 模块文档字符串 */\n",
    "        -1,              /* 保持全局状态 */\n",
    "        module_methods};\n",
    "/* Python模块初始化 */\n",
    "PyMODINIT_FUNC PyInit_mymath()\n",
    "{\n",
    "    return PyModule_Create(&mymath);\n",
    "}\n",
    "```\n",
    "\n",
    "以上源码其实只用了 C 语法。第一行指令是包含官方 Python/C API 的头文件；第一个函数 cFib 实现具体功能——递归地计算斐波那契数列的项：第一项为 0，第二项为 1，之后每一项都是其前面两项的和；其余函数都是按照规范来定义模块的信息。接下来新建文件 setup.py：\n",
    "```\n",
    "from distutils.core import setup, Extension\n",
    "mymath = Extension('mymath', sources=['mymath.cpp'])\n",
    "setup(ext_modules=[mymath])\n",
    "```\n",
    "\n",
    "输入以下命令即可调用编译器在当前目录下生成扩展模块文件，注意：在 Windows 下需要 Visual C++ Build Tools http://go.microsoft.com/fwlink/?LinkId=691126\n",
    "```\n",
    "python setup.py build_ext --inplace  # 执行时会提示实际调用的编译命令\n",
    "```\n",
    "\n",
    "最后在交互模式下测试：\n",
    "```\n",
    "In [1]: import mymath\n",
    "\n",
    "In [2]: mymath.fib?\n",
    "Docstring: calculates the fibonachi number\n",
    "Type:      builtin_function_or_method\n",
    "\n",
    "In [3]: [mymath.fib(i) for i in range(10)]\n",
    "Out[3]: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]\n",
    "```\n",
    "\n",
    "说起交互模式，其实 C/C++ 也可以有交互模式，而且还支持我们刚接触过的 Jupyter，如果需要就请安装 Cling https://github.com/root-project/cling\n",
    "![Cpp_Jupyter.png](https://upload-images.jianshu.io/upload_images/10829283-93bfa274f9a35552.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)\n"
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